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APPLIED SCIENCES

Health Outcomes after Pregnancy in Elite Athletes: A Systematic Review and Meta-analysis

KIMBER, MIRANDA L.1; MEYER, SARAH1; MCHUGH, TARA-LEIGH2; THORNTON, JANE3; KHURANA, RSHMI4; SIVAK, ALLISON5; DAVENPORT, MARGIE H.1

Author Information
Medicine & Science in Sports & Exercise: August 2021 - Volume 53 - Issue 8 - p 1739-1747
doi: 10.1249/MSS.0000000000002617

Abstract

Growing numbers of elite female athletes have made rapid comebacks to sport while adjusting to the responsibilities of motherhood and physiological changes postpartum. Although the successful return of postpartum athletes demonstrates that motherhood and elite athletic careers are not mutually exclusive, there remains a lack of evidence-based recommendations to support a safe return to sport for these athletes. In 2016, the International Olympic Committee Expert Group conducted a systematic review of the literature surrounding the health impact of return to sport in the postpartum period for elite athletes (1). Data specific to elite athletes were not found for the majority of outcomes assessed in the review; thus, the data were not synthesized as a meta-analysis and recommendations were not specific to elite athletes. As a result, return to sport plans for postpartum elite athletes continue to be largely informed by individualized guidance from coaches and medical providers (2).

The aim of this systematic review and meta-analysis was to evaluate maternal health outcomes (breastfeeding initiation [yes/no], duration of breastfeeding, postpartum weight retention or loss [change in weight from preconception], bone mineral density, low back and pelvic girdle pain [prevalence or severity], incontinence [prevalence or severity of stress, urge or mixed urinary incontinence, fecal incontinence], injury [fracture, stress fracture, sprain, strain, tendinopathy], anemia, diastasis recti, breast pain, depression, anxiety) and training patterns (<6 wk time to resume activity, training volume or intensity, performance level) of elite athletes in the postpartum period.

METHODS

This systematic review was completed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, including the completion of the checklist.

Protocol and Registration

This systematic review was registered with PROSPERO (CRD42020203253), the International Prospective Register of Systematic Reviews.

Eligibility Criteria

The population, intervention, comparison, outcome, and study design framework was used to design this study (3).

Population of interest

The population of interest was postpartum females, at any period after pregnancy, who had participated in elite-level sport immediately before or during pregnancy. Elite athletes (defined as training for or competing in national/international competitions or the highest division in their sport) before or during pregnancy were eligible for inclusion.

Intervention (exposure)

Studies were eligible for inclusion if they reported participants had competed at a national or international level or highest division in their sport before or during pregnancy.

Comparator

Eligible comparators included females who were not classified as elite athletes. This includes non–elite-level competitive athletes, recreationally active, and inactive/sedentary females. Noncomparative research designs were eligible for inclusion (i.e., case studies).

Outcomes

Outcomes of interest related to maternal health and training performance after pregnancy were selected: maternal outcomes (breastfeeding initiation [yes/no], duration of breastfeeding, postpartum weight retention or loss [change in weight from preconception], bone mineral density, low back and pelvic girdle pain [prevalence or severity], incontinence [prevalence or severity of stress, urge or mixed urinary incontinence, fecal incontinence], injury [fracture, stress fracture, sprain, strain, tendinopathy], anemia, diastasis recti, breast pain, depression, anxiety) and training (<6 wk time to resume activity, training volume or intensity, performance level).

Study design

Primary research studies of any design were eligible. Narrative or systematic reviews and commentaries were excluded. Studies that were published in languages other than English were translated using Google Translate. If deemed as potentially relevant, native speakers were contacted for translation. To include the greatest amount of data, studies that contained mixed samples of elite athletes with other nonelite athletes were accepted and labeled as a mixed group.

Literature Sources

A structured search of electronic databases was performed by a research librarian (AS) using the following databases: MEDLINE, Embase, PsycINFO, Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials, Scopus and Web of Science Core Collection, CINAHL Plus with Full-text, Child Development and Adolescent Studies, ERIC, Sport Discus, ClinicalTrials.gov, and Trip Database up to August 26, 2020 (see Supplemental Digital Content, Appendix, https://links.lww.com/MSS/C263). Reference lists of included papers were manually reviewed to identify potentially relevant studies. No language restrictions were applied.

Study Selection and Data Extraction

Two independent reviewers (MK and SM) screened titles and abstracts of all retrieved articles. Abstracts that were identified to have met the initial screening criteria by at least one reviewer were automatically retrieved for full-text screening. Full-text articles were independently screened by two reviewers for relevant outcomes before extraction. Relevant data from all publications were extracted for data synthesis. The following data were extracted from each publication: study characteristics (i.e., year, study design, country), population characteristics (i.e., number of participants, postpartum period length, pregnancy complications, age, and body mass index), exposure (i.e., type of sport and competitive level, length of exposure, and quantity of prenatal physical activity), and maternal and training outcomes. A summary of the postpartum outcomes in each paper can be found in Supplementary Table 1 (see Supplemental Digital Content, Appendix, https://links.lww.com/MSS/C263). If data were unavailable for extractions or the number of elite athletes included in the study was unknown, authors were contacted to request additional information (see Supplemental Digital Content, Appendix, https://links.lww.com/MSS/C263).

Quality Assessment (Risk of Bias)

Two reviewers (MK and SM) independently assessed the risk of bias at the individual level. We assessed methodological quality of studies based on study design using the standardized critical appraisal instruments from Joanna Briggs Institute Critical Appraisal of Evidence Effectiveness Tool (4). All studies were screened using the tool for potential sources of bias, including inappropriate sampling, flawed measurement of exposure, flawed measurements of outcomes, selective/incomplete outcomes, unidentified confounding factors, and inappropriate statistical analysis. The differences in ratings were resolved through discussion. The overall risk of bias of a study was defined as high risk when more than one-third of the factors were marked as high risk. Risk of bias tables are located in Supplementary Tables 2–4 (see Supplemental Digital Content, Appendix, https://links.lww.com/MSS/C263).

Certainty Assessment (GRADE)

The Grading of Recommendations Assessment, Development and Evaluation (GRADE) tool (5) was used to assess the certainty across studies for each postpartum maternal/training/mental health outcome. Evidence from randomized control trials (RCT) began with “high” certainty evidence, and observational studies began with a “low” certainty and was decreased for serious: 1) risk of bias (when studies with the greatest influence on the pooled results, i.e., contributed to >50% of the weight of the pool estimated); 2) inconsistency (when heterogeneity was high [I2 ≥ 50%] or when only one study was assessed); and/or 3) imprecision (when the 95% confidence interval [CI] crossed the line of no effect and was wide), such that interpretation of the data would be different if the true effect were at one end of the CI or the other. When only one study was relevant to an outcome, imprecision was not considered serious as inconsistency was already considered serious for this reason. The grading was completed independently by two reviewers (MK and SM), and differences in ratings were resolved through discussion. GRADE tables can be found in Supplementary Tables 5–13 (see Supplemental Digital Content, Appendix, https://links.lww.com/MSS/C263).

Statistical Analysis

Review Manager V.5.3 (Cochrane Collaboration, Copenhagen, Denmark) was used to conduct the statistical analyses and create the forest plots. We calculated odds ratios (OR) and 95% CI using the random-effect model with inverse variance. Statistical significance was set at a P value of <0.05. For continuous outcomes, mean differences between elite athletes and active/sedentary control groups were calculated. Because of the limited amount of included studies (n = 11), all study designs were combined for analysis.

For outcomes where a meta-analysis was not possible, results were presented as a narrative synthesis, structured around each outcome. Studies were not included in meta-analyses if data were reported incomplete (e.g., SD, SE, or number of cases/controls not provided), if data were adjusted for confounding factors, or if the study did not include a nonelite athlete control group. If data were unavailable for extraction (i.e., not reported), the authors were contacted to request additional information.

RESULTS

Study Characteristics

A PRISMA diagram of the study search and selection process is shown in Figure 1. Four studies were checked for eligibility using Google Translate; however, they were all reviews, and a native translator was not required to further assess eligibility. Eleven unique studies (4 case reports, 6 cross-sectional, 1 case–control) from six countries (Norway, Switzerland, Wales, Denmark, Bulgaria, and United States) were included in this review. The defined postpartum period varied from 6 wk to 2 yr postpartum (1,6–11) (four studies did not report weeks/months postpartum). Seven studies reported parity of participants, n = 55 elite athletes were nulliparous and n = 8 were multiparous (6,8–10,12). Mean parity reported ranged from 1.55 to 2.5 for elite athletes and 1.83 for controls (13,14). Exposure to elite-level sport ranged from 10 to 20 yr (6,8,9,11) (seven studies did not report duration of exposure to elite sport). Athletes participated in a variety of elite sports, including swimming (12), track and field (12), road racing (12), soccer (10,14), handball (14), running (7,13,15), 400-m sprint (6), orienteering (15), cross-country skiing (9,15), speed skating (15), aesthetic sports (10), weight class sports (10), technical sports (10), gymnastic (16), skiing (16), swimming (11), track and field (11), and volleyball (11). Across all included studies, 482 females were included (372 elite athletes and 110 nonelite active/sedentary controls). Two studies included a mixed sample of elite and nonelite athletes. One study (n = 110) included 35 elite athletes (31.8%) (13); however, the number of elite athletes was not reported in a second study, but the author confirmed by e-mail that athletes competing at the national/international level were included in their sample (12). Results from the included studies are presented below. A cross-sectional and case–control study were eligible for meta-analysis (10,14). The remaining nine studies (four case studies [6–9] and five cross-sectional [11–13,15,16]) were reported narratively as comparisons could not be made. No outcome had 10 or more publications; as such, publication bias was not deemed estimable and therefore rated down.

F1
FIGURE 1:
Study flow diagram.

Certainty of Evidence

Overall, the certainty of evidence from the included studies was “very low” to “low.” Evidence was downgraded for 1) risk of bias (one study contributed to >50% of the weight of the pooled estimate), 2) inconsistency due to high heterogeneity (I2 > 50%) or where heterogeneity was not estimable (i.e., one study in the forest plot), and 3) imprecision (wide CI).

Maternal Postpartum Outcomes

Initiation of breastfeeding

There was “very low” certainty evidence from one study (n = 77, downgraded for risk of bias and inconsistency [14]), demonstrating no association between prepregnancy elite athletic exposure and initiation of breastfeeding postpartum (n = 77, 1 study, OR = 0.42, 95% CI = 0.07–2.70; see Supplementary Figure 1, Supplemental Digital Content, Appendix, https://links.lww.com/MSS/C263).

Duration of breastfeeding

There was “very low” certainty evidence from two studies (n = 227, downgraded for risk of bias and inconsistency [14,16]), demonstrating no association between prepregnancy elite athletic exposure and length of breastfeeding postpartum (n = 77, 1 study; MD = −0.10, 95% CI = −2.96 to 2.76; see Supplementary Figure 2, Supplemental Digital Content, Appendix, https://links.lww.com/MSS/C263). A study that could not be included in the pooled analysis as a comparator was not included; n = 150 reported breastfeeding ranged from 4 to 9 months among elite athletes (16).

Breast pain

There was “very low” certainty evidence from one study (n = 26, downgraded for inconsistency [12]; see Supplementary Table 6, Supplemental Digital Content, Appendix, https://links.lww.com/MSS/C263) reporting on breast pain that could not be included in the pooled analysis as there was no comparator. Beilock et al. (n = 26) reported that six elite athletes indicated breast sensitivity as a barrier to training postpartum (12).

Stress urinary incontinence

There was “very low” certainty evidence from two studies (n = 145, downgraded for risk of bias and imprecision [10,14]), demonstrating no association between prepregnancy elite athletic exposure and stress urinary incontinence postpartum (n = 145, 2 studies, OR = 0.83, 95% CI = 0.39–1.76, I2 = 0%; see Supplementary Figure 3, Supplemental Digital Content, Appendix, https://links.lww.com/MSS/C263).

Urge urinary incontinence

There was “very low” certainty evidence from one study (n = 77, downgraded for risk of bias and inconsistency [14]), demonstrating no association between prepregnancy elite athletic exposure and urge incontinence postpartum (n = 77, 1 study, OR = 0.99, 95% CI = 0.25–3.83; see Supplementary Figure 4, Supplemental Digital Content, Appendix, https://links.lww.com/MSS/C263).

Mixed urinary incontinence

There was “very low” certainty evidence from one study (n = 77, downgraded for risk of bias and inconsistency [14]), demonstrating no association between prepregnancy elite athletic exposure and mixed urinary incontinence postpartum (n = 77, 1 study, OR = 0.71, 95% CI = 0.16–3.10; see Supplementary Figure 5, Supplemental Digital Content, Appendix, https://links.lww.com/MSS/C263).

Fecal incontinence

There was “very low” certainty evidence from one study (n = 77, downgraded for risk of bias and inconsistency [14]), demonstrating no association between prepregnancy elite athletic exposure and fecal incontinence postpartum (n = 77, 1 study, OR = 0.43, 95% CI = 0.02–0.88; see Supplementary Figure 6, Supplemental Digital Content, Appendix, https://links.lww.com/MSS/C263).

Injury

There was “very low” certainty evidence from three studies (n = 179, downgraded for risk of bias and inconsistency [9,10,13]), demonstrating no association between prepregnancy elite athletic exposure and postpartum injuries (n = 68, 1 study, OR = 10.18, 95% CI = 0.53–196.87; see Supplementary Figure 7, Supplemental Digital Content, Appendix, https://links.lww.com/MSS/C263). Two studies (n = 111) could not be included in the pooled estimates due to no comparison group. One study (n = 110) reported nine females sustained running injuries while breastfeeding; this sample included only 31.8% of elite athletes (n = 35), and it was not reported specifically how many elite athletes experienced injuries postpartum (13). One case study (n = 1) reported that a cross-country skiing athlete sustained two sacral fractures while 13–24 wk postpartum (9).

Bone mineral density

There was “very low” certainty evidence from one study (n = 1, downgraded for inconsistency; (9); see Supplementary Table 9, Supplemental Digital Content, Appendix, https://links.lww.com/MSS/C263), reporting that the bone mineral density of a cross-country skier decreased from prepregnancy (1.298 g·cm−2) to postpartum. Bone mineral density was 1.199 g·cm−2 between 1 and 6 wk postpartum, 1.154 g·cm−2 between 13 and 18 wk postpartum, 1.237 g·cm−2 between 25 and 44 wk postpartum, and 1.250 g·cm−2 between 54 and 61 wk postpartum (9).

Low back and pelvic girdle pain

There was “very low” certainty evidence from one study (n = 77, downgraded for risk of bias and uncertainty [14]), demonstrating no association between prepregnancy elite athletic exposure and low back pain (n = 77, 1 study, OR = 0.60, 95% CI = 0.14–2.51; see Supplementary Figure 8, Supplemental Digital Content, Appendix, https://links.lww.com/MSS/C263), low back pain with radiation (n = 77, 1 study, OR = 0.99, 95% CI = 0.25–3.83; see Supplementary Figure 9, Supplemental Digital Content, Appendix, https://links.lww.com/MSS/C263), pelvic girdle pain (sacroiliac joints) (n = 77, 1 study, OR = 0.99, 95% CI = 0.25–3.83; see Supplementary Figure 10, Supplemental Digital Content, Appendix, https://links.lww.com/MSS/C263), pelvic girdle pain (pubic symphysis) (n = 77, 1 study, OR = 1.39, 95% CI = 0.44–4.31; see Supplementary Figure 11, Supplemental Digital Content, Appendix, https://links.lww.com/MSS/C263), or pelvic girdle pain (sacroiliac joints and pubic symphysis) (n = 77, 1 study, OR = 1.56, 95% CI = 0.36–6.75; see Supplementary Figure 12, Supplemental Digital Content, Appendix, https://links.lww.com/MSS/C263).

Training Patterns and Performance Postpartum

Less than 6 wk return to physical activity

There was “very low” certainty evidence from nine studies (n = 422, downgraded for risk of bias and inconsistency [1,6–11,13,16]), demonstrating a positive association between prepregnancy elite athletic exposure and a <6 wk return to physical activity postpartum (n = 145, 2 studies, OR = 6.93, 95% CI = 2.73–17.63, I2 = 11%; Fig. 2). Seven studies (n = 277) could not be included in the pooled estimates due to lack of comparator group. One study (n = 110) reported that 73 females returned to running in under 6 wk; however, this study is limited by only 31.8% of elite athlete representation within the sample as described above (13). A case study (n = 1) reported a marathoner began moderate cycling 8.5 d after twin gestation (7). Another case study (n = 1) reported a cross-country skiing athlete began low-intensity running/walking within the first week postpartum and progressively increased training volume to 11 h·wk−1 by the fourth week postpartum (9). A case study (n = 1) reported that a postpartum athlete returned to her usual conditioning and performance training (sprinting and running program) several weeks after delivery; a specific time period was not reported (6). Potteigher et al. (n = 1) reported the training of a postpartum marathon runner who began marathon training (68 km·wk−1) at 4 wk postpartum and competed in the Olympic Marathon Trials at 16 wk postpartum (8). Zaharieva (16) reported elite athletes (n = 150) resumed their sporting activities between 2 and 5 months postpartum and began competing again at 3–8 months postpartum. A cross-sectional study (n = 13) reported Olympic athletes began training between 3 and 6 months after delivery (11).

F2
FIGURE 2:
Effects of prepregnancy elite athletic experience vs controls (active/sedentary) on <6 wk return to activity. Data are reported as OR. Analysis conducted using a random-effect model. IV, inverse variance.

Endurance training volume postpartum

There was “low” certainty evidence from three studies (n = 134 females [9,10,14]) for a positive association between elite athletic exposure before or during pregnancy and increased endurance training volume postpartum (n = 102, 1 study, MD = 533.70 min·wk−1, 95% CI = 451.42–615.99, I2 = 65%; see Supplementary Figure 13, Supplemental Digital Content, Appendix, https://links.lww.com/MSS/C263). Two studies (n = 32) could not be included in the pooled estimate due to lack of comparator group. One case study (n = 1) reported the postpartum training hours of a cross-country skier. Between weeks 1 and 6 postpartum, the athlete’s mean training hours were 6.6 ± 3.8 h·wk−1, which increased progressively until 13–18 wk postpartum when the athlete sustained a sacral stress fracture. By 54–61 wk postpartum, the athlete was completing 16.9 ± 3.5 h·wk−1 (9). One cross-sectional study (n = 31) reported that mean training hours were 4 ± 3.6 h·wk−1 at 6 wk postpartum among the athletes, compared with 14 ± 6.7 h·wk−1 before pregnancy (14).

Strength training volume postpartum

There was “very low” certainty evidence from one study (n = 102 females, downgraded for inconsistency [10]), demonstrating a positive association between elite athletic exposure before or during pregnancy and increased strength training volume postpartum (n = 102, 1 study, MD = 74.20 min·wk−1, 95% CI = 38.69–109.72, I2 = 95%; see Supplementary Figure 14, Supplemental Digital Content, Appendix, https://links.lww.com/MSS/C263).

Intensity of training postpartum

There was “very low” certainty evidence from one study (n = 1, downgraded for inconsistency [9]; see Supplementary Table 12, Supplemental Digital Content, Appendix, https://links.lww.com/MSS/C263). One case study (n = 1) reported the intensity of training completed between 1 and 61 wk postpartum. Between 1 and 6 wk postpartum, the athlete engaged in dominantly low-intensity endurance training (6.1 ± 3.6 h·wk−1) and a small amount of strength training (0.5 ± 0.6 h·wk−1). Moderate- and high-intensity endurance training began between 7 and 12 wk postpartum but was stopped due to a sacral fracture and then was permanently reintroduced at 30 wk postpartum (9).

Improved performance postpartum

There was “very low” certainty evidence from five studies (n = 262, downgraded for risk of bias and inconsistency [6,10,11,15,16]), suggesting that athletes participating in elite sport before pregnancy may experience improved performance in the postpartum period. Although the pooled estimate found no association (n = 68, 1 study, OR = 2.76, 95% CI = 0.50–15.33; see Supplementary Figure 15, Supplemental Digital Content, Appendix, https://links.lww.com/MSS/C263), four studies (n = 194) that could not be included in the pooled estimates demonstrated that 52.1% of elite athletes experienced improved performance postpartum. One case study (n = 1) reported on a postpartum athlete who surpassed her previous personal best in several short-distance runs in the first 6 months postdelivery (6). Another study (n = 30) reported that two athletes placed better in competitions postpartum compared with prepregnancy (15). A cross-sectional study (n = 150) reported that 88 athletes improved former prepregnancy competition records, and 22.2% of athletes indicated feeling more fit after childbirth than before (16). A cross-sectional study (n = 13) reported that six Olympic athletes improved their results in the year after delivery, and four Olympic athletes bettered their results between the first and the second year postpartum (11). It is important to note that the length of time between delivery and competition date postpartum was not reported in two studies (15,16).

Reduced performance postpartum

There was “very low” certainty evidence from three studies (n = 248, downgraded for risk of bias and inconsistency [10,15,16]), demonstrating no association between prepregnancy elite athletic exposure and reduced performance postpartum (n = 68, 1 study, OR = 2.70, 95% CI = 0.74–9.83; see Supplementary Figure 16, Supplemental Digital Content, Appendix, https://links.lww.com/MSS/C263). Two studies (n = 180) could not be included in pooled estimates due to lack of comparator group. One study (n = 30) reported that five athletes placed worse in competitions postpartum compared with prepregnancy (15). A cross-sectional study (n = 150) reported that 59 elite athletes did not reach their athletic records attained before pregnancy (16). Both studies did not report the period between delivery and competition or record used to determine performance postpartum.

Other outcomes

No study reported on weight gain or loss postpartum, anemia, diastasis recti, and postpartum depression or anxiety.

DISCUSSION

Pregnancy no longer marks the end of an athlete’s career, and many elite athletes not only return to sport but are breaking personal and world records as new moms. Although athletes have demonstrated performance after pregnancy is possible, there is very little guidance on how or when to return to sport postpartum. The purpose of this review was to evaluate the effect of elite athletic exposure before or during pregnancy on postpartum health and training outcomes. Our study found “very low” quality evidence from 11 studies, indicating elite postpartum athletes have increased odds of returning to physical activity before 6 wk postpartum compared with controls. Because of limited available data, we were not able to assess whether an earlier return to sport was linked to an increased risk of injury or altered performance in the postpartum period.

Although postpartum females are typically advised to avoid high-intensity, high-impact exercise for 6 wk after delivery (1), a recently published guideline recommends extending this to a minimum of 12 wk to ensure adequate healing and strengthening of pelvic floor and core muscles has been achieved (17). Our data demonstrate that elite athletes have increased odds of returning to physical activity in the early postpartum period. Return to sport is influenced by several physical and psychological factors, including gestational complications, type of delivery (vaginal, surgical, and instrumental), pelvic floor dysfunction, pain, depression, and health of one’s new child. A recent review found “very low” quality evidence that pregnancy outcomes were not different between pregnant elite athletes and nonelite athlete controls (18). After delivery, we found “very low” quality evidence from one study identifying no associations between engaging in elite sport before or during pregnancy with the development of urinary or fecal incontinence and low back or pelvic girdle pain (no study reported on postpartum depression or anxiety). Although further high-quality studies are needed, combined, these data hint that differences in health outcomes did not influence return to sport. Although outside the scope of this review, external influences, including the timing of major sporting competitions or qualifying events, as well as contracts with sporting agencies or corporate sponsors may also contribute to a quicker return to sport. A paid leave of absence during or after pregnancy is uncommon for elite female athletes, resulting in significant reductions in income. As such, postpartum athletes may face financial pressures to return to training promptly so they may continue with their careers (19,20). There are a multitude of other contributing factors to a <6 wk return to physical activity among elite athletes; further research is needed to understand the influence of physical, psychological, and social factors.

A key concern identified in this review is the rate and nature of injury among postpartum elite athletes. “Very low” quality evidence from three studies (n = 179) identified that 16 injuries were sustained among 14 athletes (7 stress fractures [sacrum, tibia, fifth metatarsal], 9 “running injuries”) (9,10,13). An increased risk of injury in the postpartum period has been suggested to result from elevated joint laxity during pregnancy and breastfeeding. It is theorized that the hormonal adaptations during pregnancy and postpartum, including increased levels of estrogen, relaxin, and progesterone, cause increased laxity within joint capsules and connective tissues (21), which may increase a female’s risk of injury during and after pregnancy. Although the extent to which hormone levels contribute to heightened joint laxity postpartum is not completely understood (22,23), significant increases in joint laxity among postpartum females has been observed (22,24). One case study included in this review reported that an elite cross-country skiing athlete sustained two sacral stress fractures, which occurred in conjunction with progressions to her training program and her lowest bone mineral density value postpartum (9). Another study (n = 68; elite n = 34, control n = 34) found five stress fractures (three sacrum, one tibia, and one fifth metatarsal) were sustained among n = 4 elite athletes in the first 9 months postpartum, whereas controls did not report any injuries. Further, the volume of endurance and strength training postpartum was four to six times greater among elite athletes at 0–3, 3–6, and 6–9 months postpartum (P < 0.001) compared with controls (10). These data suggest that the rate of injury postpartum may be higher among elite athletes who engage in high volumes of training postpartum.

Stress fractures occur in 9%–13% of female athletes (25,26). Although our review demonstrates that 2.8% of elite athletes sustained stress fractures, of concern is the high proportion of sacral stress fractures. Sacral stress fractures accounted for 43.8% of reported injuries but are a rare occurrence among nonpregnant athletes and have only been reported in few case reports (27–32). Although still uncommon, this injury has also been observed among postpartum females (33–36) due, in part, to high amounts of maternal calcium transfer in breastmilk, causing 3%–10% reduction in bone mineral density during breastfeeding (37,38). Importantly, all athletes who reported stress fractures in the current review were breastfeeding. Risk factors for sustaining a sacral stress fracture include sex and engagement in high-impact sports; the injury is commonly seen in runners, volleyball, tennis, and basketball players (39). Among the included studies, sacral stress fractures were observed in two team ball sport and two endurance type athletes (10), aligning with evidence of a higher prevalence among high-impact sports. Our review demonstrates that rates of sacral stress fractures are higher among postpartum elite athletes, which may be associated with adaptations during pregnancy and the postpartum period, and a return to activity early postpartum may exacerbate this risk. Further research is urgently needed to understand if risk of injury is higher for postpartum elite athletes and any effects of rapid resumption of activity and breastfeeding.

Although several high-profile athletes gained significant media attention for achieving personal best performances after birth, empirical evidence of an ergogenic effect of pregnancy remains inconclusive (40). In the current review, four studies (n = 262) demonstrated improved performance in n = 101 (40.5%) of elite athletes postpartum. Comparatively, three studies (n = 248) reported that n = 73 (29%) of elite athletes demonstrated reductions in performance postpartum. It is important to note that the method of determining performance level differed among the included studies; one study asked athletes if they “felt a change in performance level from prepregnancy” (10), whereas four studies used placements in competitions or personal records from prepregnancy to postpartum as indicator of performance (6,11,15,16). These results suggest that elite athletes may experience improved performance postpartum. Importantly, fewer athletes reported detriments to their performance after pregnancy. It is theorized that performance postpartum may improve due to the physiological adaptations to pregnancy, such as increased cardiac output and blood volume (41), which would theoretically improve aerobic performance. These physiological adaptations are balanced by potentially lower-quality sleep and/or access to childcare support, which could also affect performance. A key limitation of these data is that the time between delivery and reporting of performance was not often reported. Therefore, it cannot be determined at which point elite athletes may be experiencing improvement or decrements in postpartum performance.

Strengths and limitations

The strengths of the present review were the methodological standards (PRISMA and GRADE) used in guiding the systematic review process. All study types (excluding narratives, systematic reviews, and commentaries) were included in this review, and a diverse group of outcomes were selected to complete a comprehensive review of postpartum maternal and training outcomes of elite athletes.

A key limitation of this review is the limited ability to draw conclusions from this review due to solely “very low” to “low” quality evidence. No RCT was included in this review, likely due to difficulties in conducting RCT in this population (i.e., disruptions to training programs and ethical concerns). Further, only two studies included comparator groups and thus were included in a meta-analysis increasing between-study heterogeneity and bias of results. To understand the relationship between prepregnancy or during pregnancy elite athlete experience and postpartum outcomes, additional studies of higher quality are required. Several pelvic health outcomes were not assessed in this review, including pelvic organ prolapse and pain, which are critical indicators of pelvic health and may be negatively affected through rapid return to exercise postpartum. Future research is urgently needed to address pelvic health in postpartum athletes. The majority of studies included were retrospective in design, which decreases the validity of the results through subjective bias and recall. Further, all included studies are observational and automatically deemed “low” quality evidence per GRADE standards. Several studies did not define a postpartum period, and therefore we did not define a period for this review to include as many studies as possible; as a result, conclusions surrounding the onset of the reviewed outcomes cannot be determined. Not all studies included measurements of physical activity before or during pregnancy. The sample sizes were small among the included studies, which increases the likelihood of a type II error. Two studies included contained a mixed sample of recreational and elite athletes, limiting the applicability of the findings. Lastly, all the studies were conducted in Western societies, which limit the generalizability of these findings to postpartum athletes outside of these regions. Future studies are required to identify associations between elite athletic experience and postpartum outcomes to better support a safe return to sport after pregnancy in elite athletes.

CONCLUSION

Engaging in elite-level sport before or during pregnancy is associated with “very low” certainty evidence of increased odds of a less than 6 wk return to activity and “low” certainty evidence of higher training volume postpartum compared with active/sedentary controls. “Very low” certainty evidence suggests that pregnancy does not impair performance postpartum, and greater numbers of elite athlete report improved performance after pregnancy. Lastly, “very low” certainty evidence suggests that postpartum elite athletes may have increased rates of injury, which may be exacerbated by a rapid return to and progression of activity postpartum. Limited data suggest that elite sporting exposure before or during pregnancy is not associated with initiation of breastfeeding, duration of breastfeeding, urinary or fecal incontinence, and low back and pelvic girdle pain. Additional high-quality studies are urgently needed to better understand these associations to provide evidence-based recommendations so female elite athletes may return to sport safely.

M. H. D. is funded by the Christenson Professorship in Active Healthy Living, a Heart and Stroke Foundation of Canada (HSFC)/Health Canada Improving Heart Health for Women Award, National and Alberta HSFC New Investigator Award. There are no other funding sources. The authors do not have any conflicts of interest to declare. The results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. The results of the study do not constitute endorsement by the American College of Sports Medicine.

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Keywords:

RETURN TO SPORT; ATHLETE; MATERNAL; TRAINING; POSTNATAL

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