Prevalence and association with birth outcomes of low vitamin D levels among pregnant women living with HIV : AIDS

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Epidemiology and Social: CONCISE COMMUNICATION

Prevalence and association with birth outcomes of low vitamin D levels among pregnant women living with HIV

Bergløv, Annea; Moseholm, Ellena; Katzenstein, Terese L.b; Johansen, Isik S.c; Storgaard, Mereted; Pedersen, Gittee; Weis, Ninaa,f

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AIDS 35(9):p 1491-1496, July 15, 2021. | DOI: 10.1097/QAD.0000000000002899



Low vitamin D level during pregnancy, in women without HIV, has been associated with a number of adverse maternal and neonatal outcomes, such as preeclampsia, gestational diabetes, small-for-gestational-age (SGA), low birth weight and respiratory infections in childhood [1–4].

People with HIV (PHIV) might have an increased risk of vitamin D insufficiency compared with individuals living without HIV [5–7], probably because of a combination of more traditional factors, such as lack of sun exposure and malabsorption of vitamin D as well as treatment with combined anti-retroviral therapy (cART) [8,9].

Vitamin D is an immune regulatory hormone. In vivo, it has been demonstrated to affect the CD4+ Th1--Th2 balance, inhibiting Th1 and augmenting Th2 cell development [10] and Th2 enhanced cytokine expression [11]. Further vitamin D also plays a role in the control of intracellular infections [12,13].

The literature on vitamin D in pregnancy among well treated WLWH living in developed countries is limited. Thus, the aim of this study was primarily to evaluate the prevalence of low vitamin D levels among well treated pregnant WLWH in Denmark, and secondarily to identify risk factors for low vitamin D levels and to assess the association between vitamin D status and birth outcomes.



The Danish population consists of 5.7 million inhabitants with an estimated adult HIV prevalence of 0.1% [14,15]. In Denmark, WLWH are followed at eight specialized centers during pregnancy and four specialized centers for delivery. Their children are followed at four affiliated pediatric units. cART is provided free of charge to all residents in Denmark with HIV, and most WLWH (84% in this study) are well treated with undetectable viral loads [16].

Study population

From the Danish HIV Birth Cohort (DHBC), all WLWH giving birth to one or more singleton children in Denmark in the period 2000–2018 with a vitamin D measurement during pregnancy were identified.

The Danish HIV birth cohort

Danish HIV birth cohort (DHBC) is a nationwide database including all pregnant WLWH, followed at Danish HIV treatment clinics since year 2000 and their infants. The Danish HIV treatment clinics are located at Copenhagen University Hospitals, Hvidovre and Rigshospitalet, Odense University Hospital, Aalborg University Hospital and Aarhus University Hospital, Skejby.

Blood samples

Not all women had blood analyzed for vitamin D during pregnancy. Additional blood samples, drawn from the women at a routine outpatient clinic visit during their pregnancy, available at the research biobank at the Department of Infectious Diseases, Copenhagen University Hospital, Hvidovre, were analyzed for 25-hydroxyvitamin D (25(OH)D) (n = 78).

All patients included in DHBC give consent to the use of their blood samples in research.

Vitamin D analysis were performed by radioimmunoassays (2000–2012) and chemiluminescence assays (2012–2018), respectively. The blood samples were tested for vitamin D levels on a COBAS 8000 analyzer robot (Roche Diagnostics, Indianapolis, Indiana, USA). Inter-assay variability did not exceed 12%.

Vitamin D

We defined vitamin D deficiency as 25(OH)D concentrations less than 26 nmol/l, insufficiency as 50 nmol/l or less and sufficiency as greater than 50 nmol/l. In some analysis, vitamin D was defined by two categories 50 mmol/l or less and greater than 50 mmol/l.

Birth outcomes

We defined preterm birth as gestational age less than 37 weeks [17], low birth weight as weight less than 2500 g [18] and small-for-gestational age as weight less than 10th percentile for gestational age by sex using the WHO fetal growth charts [19].

Statistical models

Categorical variables were described in percentages and continuous variables were described as means [± standard deviation (SD)]. Baseline characteristics were summarized and compared between women with -- versus without a vitamin D measurement during pregnancy and compared between women with insufficient -- versus sufficient vitamin D levels (≤50 versus >50 nmol/l), using Pearson's χ2 or Student unpaired t test as appropriate. A sensitivity analysis was performed, excluding participants who had frozen specimens obtained.

Risk factors for low vitamin D levels were assessed using log-binomial regression models, both univariate and adjusted for maternal-related and HIV-related factors. We examined the following risk factors for low vitamin D levels: maternal age, maternal region of birth, CD4+ cell count, HIV RNA, cART regime, smoking, season of vitamin D measurement and BMI. Multivariate models were adjusted for maternal age, maternal region of birth and HIV RNA. Univariate models included a missing category, whereas individuals with missing explanatory values were excluded from the multivariable analyses.

The association between vitamin D status and birth outcomes was assessed using linear regression models for continuous outcomes and log-binomial models for binary outcomes. Multivariate models were adjusted for maternal age, maternal region of birth, HIV RNA, smoking and sex of the infant. All models were also adjusted for intragroup correlations in children born to the same mother.


Study population

By the end of December 2018, 563 infants, born to 401 mothers, were included in the DHBC. In total, 208 (37%) WLWH had information available regarding vitamin D levels during pregnancy of whom 130 (23%) had blood samples analyzed during pregnancy and 78 (13.9%) had measurements from frozen specimens obtained during pregnancy. Of the 208 women with available data on vitamin D, 13% had vitamin D deficiency, 34% had vitamin D insufficiency and 53% had sufficient vitamin D level. Of the 208 WLWH, 43% had their vitamin D levels measured from first trimester blood samples, 36% second trimester blood samples and 21% from third trimester blood samples. Table 1 shows the characteristics of the cohort. Supplementary Table 1, presents the characteristics of the 208 WLWH with available vitamin D levels.

Table 1 - Maternal and infant characteristics in 563 pregnancies among women living with HIV in Denmark (2000–2018) with and without vitamin D status.
Total number (%)a (n = 563) Women with vitamin D [No. (%)]a (n = 208) Women without vitamin D [No. (%)]a (n = 355) P value
Maternal age
 Mean in years ± SD 32.4 ± 5.4 32.7 ± 5.3 32.2 ± 5.4 0.37
Maternal region of birth 0.07
 Denmark 125 (22) 36 (17) 89 (25)
 Africa 325 (58) 135 (65) 190 (54)
 Asia 67 (12) 23 (11) 44 (12)
 Other/unknown 46 (8) 14 (7) 32 (9)
CD4+ cell count prior to delivery 0.23
 ≥500 cells/μl 235 (42) 95 (46) 140 (39)
 300--499 cells/μl 173 (31) 75 (36) 97 (27)
 <300 cells/μl 68 (12) 30 (14) 38 (11)
 CD4+ cell count information missing 88 (15) 8 (4) 80 (23)
HIV RNA viral load prior to delivery 0.77
 <50 copies/ml 471 (84) 181 (87) 290 (82)
 ≥50 copies/ml 62 (11) 25 (12) 37 (10)
 HIV RNA viral load information missing 30 (5) 2 (1) 28 (8)
Prepregnancy BMI
 Mean in kg/m2 ± SD 24.6 ± 5.1 24.3 ± 5 24.6 ± 6 0.79
 Prepregnancy BMI information missing 386 (69) 63 (30) 323 (91)
Maternal smoking in pregnancy
 Yes 87 (15) 28 (13) 49 (17) 0.08
 Smoking information missing 47 (9) 5 (2) 42 (12)
Preterm Birth (<37 weeks)
 Yes 50 (9) 20 (10) 30 (8) 0.94
 Gestational age information missing 72 (13) 9 (04) 63 (18)
Birth weight
 Mean in gram ± SD 3181 ± 613.8 3199 ± 631.5 3170 ± 616.3 0.61
 Birth weight information missing 49 (9) 14 (7) 32 (10)
aData represent no. (%) of women unless otherwise specified.
Significant P less than 0.05.

Women with a vitamin D measurement in pregnancy

WLWH who had blood analyzed at a clinical visit during pregnancy had a higher mean age and BMI and were more likely to be of African origin compared with WLWH for whom frozen specimens were analyzed. There was no difference between the two groups in regard to the prevalence of vitamin D deficiency and insufficiency (Supplementary Table 2, As presented in Supplementary Table 3,, less than 9% of WLWH had vitamin D status measured per year during pregnancy in the time period 2000–2009, versus 25--60% of WLWH during 2010--2018.

Risk factors for low vitamin D level

As presented in Table 2, being of African origin [relative risk (RR) 2.68], Asian origin (RR 3.38), and having HIV RNA levels greater than 50 copies/ml (RR 1.43) was associated with an increased risk of low vitamin D level in the multivariable models.

Table 2 - Risk factors of low vitamin D status (25 (OH)D ≤50 nmol/l) among 208 pregnant women living with HIV in Denmark (2000–2018).
Relative Risk [95% CI] Relative Risk [95% CI]
n Univariate P value Multivariatea P value
Maternal age
 Less than 30 years 60 Ref Ref
 30–39 years 131 0.85 [0.62--1.15] 0.29 0.92 [0.68--1.23] 0.56
 40 years or older 17 0.53 [0.24--1.19] 0.12 0.63 [0.30--1.31] 0.22
Maternal region of birth
 Denmark 36 Ref Ref
 Africa 135 2.78 [1.37--5.63] <0.01 2.68 [1.23--5.83] 0.01
 Asia 23 3.13 [1.44--6.77] <0.01 3.38 [1.49--7.69] <0.01
 Other/unknown 14 1.84 [0.69--4.87] 0.22 1.92 [0.69--5.34] 0.21
CD4+ cell count third trimester
 ≥500 cells/μl 95 Ref Ref
 300--499 cells/μl 75 1.00 [0.71--1.40] 0.99 0.66 [0.50--0.86] <0.01
 <300 cells/μl 30 1.33 [0.91--1.92] 0.13 0.70 [0.49--0.99] 0.04
 Missing 8
HIV RNA third trimester
 <50 copies/ml 181 Ref Ref
 ≥50 copies/ml 25 1.65 [1.20--2.26] <0.01 1.43 [1.01--2.03] 0.04
 Missing 2
ART treatment initiated
 Prior to pregnancy 142 Ref ref
 During pregnancy 65 1.27 [0.95--1.69] 0.11 1.20 [0.90--1.60] 0.2
 Missing 1
Treatment category
 NRTI + PI 152 Ref Ref
 NRTI + NNRTI 22 0.62 [0.32--1.18] 0.14 0.70 [0.39--1.26] 0.24
 NRTI + INST 12 1.01 [0.57--1.80] 0.96 1.09 [0.67--1.79] 0.72
 Other 22 1.06 [0.68--1.64] 0.79 1.30 [1.00--1.68] 0.05
Prepregnancy BMI
 <18.5 12 1.33 [0.75--2.35] 0.33 1.03 [0.59--1.80] 0.92
 18.5–25 73 Ref Ref
 >25 60 1.27 [0.88--1.83] 0.2 1.19 [0.84--1.67] 0.33
 Missing 63
Maternal smoking in pregnancy
 No 175 Ref Ref
 Yes 28 0.99 [0.63--1.57] 0.97 0.94 [0.60--1.48] 0.8
 Missing 5
Season for vitamin D
 Spring 49 Ref Ref
 Summer 42 0.85 [0.52--1.39] 0.52 0.68 [0.42--1.10] 0.12
 Autumn 58 1.15 [0.79--1.67] 0.46 0.90 [0.64--1.25] 0.53
 Winter 57 1.17 [0.79--1.73] 0.43 1.00 [0.71--1.42] 1.00
CI, confidence interval; NRTI, nucleoside/nucleotide reverse transcriptase inhibitor; PI, protease inhibitor; NNRTI, non-nucleoside reverse transcriptase inhibitor; INST, integrase inhibitor. P-values in bold are significant.
aAdjusted for maternal age, maternal country of birth, and HIV RNA at delivery.

Vitamin D status and birth outcomes

The association between vitamin D status and birth outcomes is presented in Supplementary Table 4, WLWH with vitamin D deficiency had an increased risk of preterm birth (RR 2.66) and SGA (RR 6.83), compared with WLWH with sufficient vitamin D levels.


In this nationwide cohort study of WLWH in Denmark, who gave birth from 2000 to 2018, we found that of 208 women with available vitamin D levels included in the study, 13% had vitamin D deficiency, 34% had vitamin D insufficiency and 53% had sufficient vitamin D levels.

We found that being of African or Asian origin was associated with an increased risk of low vitamin D level. Further, we found an association between having HIV RNA levels greater than 50 copies/ml and low vitamin D level. Importantly, we found that WLWH with vitamin D deficiency had an increased risk of preterm birth and of giving birth to infants who were SGA compared with WLWH with sufficient vitamin D level. The relatively small sample size likely led to inadequate power to detect any differences in continuous outcomes, such as birthweight and gestational age.

The association between low vitamin D level and African or Asian origin in pregnant women living in Northern countries has been reported in other studies [20,21]. A Swedish study found an increased odds ratio (OR) of having vitamin D deficiency if the women were born in Asia or Africa (OR of 22.09 and 9.74, respectively) compared with women born in North Europe. A Norwegian study found that women from South Asia, the Middle East and sub-Saharan Africa had significantly lower vitamin D levels during their pregnancy relative to women born in Norway [20]. They found determinants of vitamin D deficiency were not taking vitamin D supplements, lack of sun exposure and low age [20,21].

Some studies have found that individuals of United States of African descent have lower vitamin D-binding globulins (VDBG), which in turn leads to normal levels of bioavailable vitamin D [22]. However, this analysis is not available in our clinic.

Similar to our study, Kim et al.[9] found that detectable HIV viremia (>50 copies/ml) was associated with low vitamin D level as well as a missing association between cART and low vitamin D level. However, other studies have found an association between cART and low vitamin D level, especially treatment with Efavirenz or Tenofovir [23,24]. The mechanism behind has not yet been clarified [23,24]. Tough alterations in the kidney, such as renal tubular phosphate wasting causing hypophosphatemia and secondary osteomalacia, and endocrine functions, such as hyperparathyroidism, have been proposed as potential factors [25–27]. Tenofovir has been shown to reduce free 1,25(OH)2D3 levels by increasing parathyroid hormone levels and efavirenz induces cytochrome P450 enzymes, which may accelerate the catabolism of both 25(OH)D and 1,25(OH)2D3 [26].

Our findings of an association between vitamin D deficiency and an increased risk of preterm birth and SGA are in line with the literature [28,29]. Jao et al.[28] found that severe vitamin D deficiency was associated with preterm birth. It is difficult to determine whether the increased risk of preterm birth and SGA is because of low maternal vitamin D level, cART, or a combination of both, or whether low vitamin D level is a substitute for something else that might increase the risk.

This study has several strengths. First, it is a nationwide study including all WLWH who, since 2000, have given birth in Denmark. Second, the DHBC is a prospective cohort with consecutive ongoing enrollment. Third, the size of the population is similar to – or larger than – similar studies with a population of pregnant WLWH [29–31].

The study also has limitations. First, less than half of our population had their vitamin D status assessed during pregnancy, weakening the power of the results, which is underlined by the wide confidence intervals (CIs) of our significant results. Second, we do not know whether the women included in the present study used vitamin D supplements during pregnancy but the Ministry of Health does advise all pregnant women to take a supplement of 10 μg vitamin D throughout pregnancy [32]. Third, we do not have data on vitamin D-binding globulin. Lastly, a longer follow-up period would give a clearer picture of the long-term effects of low vitamin D level during pregnancy on the children.

In conclusion, WLWH of African or Asian origin and WLWH with HIV RNA levels greater than 50 copies/ml have an increased risk of having low vitamin D levels. Further, WLWH with vitamin D deficiency have an increased risk of preterm birth and SGA.


We thank the patients for their participation in the Danish HIV Birth Cohort.

Authorships: All authors contributed to the study design, data collection, data interpretation and writing the manuscript, and approved the final version. A.B. and E.M. had full access to the data and did the statistical analysis. A.B. wrote the first draft of the article and, together with N.W. and E.M., devised the original concept for the study.

The data has been presented at the 10th International Workshop on HIV and Woman on the 6 March 2020, Boston, Massachusetts, USA.

Conflicts of interest

N.W. – with no relation to the submitted work -- has been a clinical investigator, member of an advisory board or lecturer for Abbvie, Merck, BMS, Gilead and GSK and has received unrestricted grants for research or scientific meetings from Abbvie, Gilead, GSK and Novo Nordisk Foundation. E.M. reports grants from the Novo Nordisk Foundation, outside the submitted work, as well as honoraria from Gilead paid to her institution. A.B., I.J., M.S., T.K. and G.P. have no conflicts of interest.


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fetal outcomes; HIV; nationwide cohort study; pregnancy; vitamin D; women

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