A disintegrin and metalloprotease (ADAM12) is a placenta-derived multidomain glycoprotein that is thought to be involved in controlling fetal and placental growth and development. There is a short and a long form of ADAM12, and the short one, which is the circulating form, has proteolytic activity against insulin-like growth factor-binding proteins-3 and -5, thus regulating the bioavailability of insulin-like growth factor.1,2
There is some evidence that in pregnancies complicated by fetal trisomies 21 and 18 and in those destined to develop preeclampsia or deliver small for gestational age (SGA) neonates, the concentration of maternal serum ADAM12 in the first trimester of pregnancy is reduced.3–8 Laigaard et al6 reported that in pregnancies that developed preeclampsia, the median serum ADAM12 concentration at 10–14 weeks of gestation was reduced to 0.859 multiples of the median (MoM) of normal controls. Similarly, Spencer et al7 reported that in cases that developed preeclampsia, the serum ADAM12 at 11–14 weeks was 0.712 MoM and that the level was particularly low (0.498 MoM) in the cases with early-onset preeclampsia requiring delivery before 35 weeks. Another study reported that in pregnancies delivering neonates with birth weight below the 5th percentile, the median serum ADAM12 at 11–14 weeks was 0.885 MoM.8 Several studies have documented that pregnancy-associated plasma protein A, another placenta-derived insulin-like growth factor-binding proteins protease, is reduced at 11 0/7 to 13 6/7 weeks in maternal serum of pregnancies resulting in preeclampsia, SGA, and preterm delivery (Poon LC, Maiz N, Valencia C, Plasencia W, Nicolaides KH. First-trimester maternal serum PAPP-A and preeclampsia. Ultrasound Obstet Gynecol. In press).9,10
The underlying mechanism for both preeclampsia and SGA is thought to be impaired placentation due to inadequate trophoblastic invasion of the maternal spiral arteries, documented by the findings of both histologic studies and Doppler ultrasound studies of the uterine arteries.11–14 There is evidence that the severity of the fetal compromise is mainly related to the gestation of onset of preeclampsia. Thus, pathologic studies have shown that the prevalence of placental lesions in women with preeclampsia is inversely related to the gestational age at delivery.15,16 Epidemiologic studies reported that preterm preeclampsia is associated with SGA, whereas in term preeclampsia, the birth weight is often normal or increased.17,18 Doppler studies of the uterine arteries have demonstrated that the prevalence of increased pulsatility index is substantially higher in cases of preeclampsia with SGA than for preeclampsia without SGA or SGA without preeclampsia.13,14,19
The aim of this study was to investigate further the levels of maternal serum ADAM12 in the first trimester of pregnancy in cases that subsequently develop preeclampsia and/or SGA and the relation of these levels to uterine artery pulsatility index and maternal serum PAPP-A.
MATERIALS AND METHODS
This was a case-control study. In our center we performed screening for preeclampsia in women attending for routine assessment of risk for chromosomal abnormalities by measurement of fetal nuchal translucency thickness, maternal serum PAPP-A, and free β-hCG at 11 0/7 to 13 6/7 weeks of gestation.20,21 We recorded maternal characteristics and medical history and measured the uterine artery pulsatility index by transabdominal color Doppler.17 Approximately 10 mL of blood were drawn from patients to a plain BD Vacutainer (Becton, Dickinson and Company, Franklin Lakes, NJ) blood collection tube, which was left to clot at room temperature for 10–15 minutes. The blood sample was then centrifuged at 3,000g for 10 minutes and the supernatant (serum) was collected. The serum samples were stored at –20°C for the initial 8–24 hours and subsequently stored at –80°C until being analyzed. Written informed consent was obtained from the women agreeing to participate in the study, which was approved by King's College Hospital Ethics Committee.
The base cohort study population, wherein the present case-control study was nested, was examined between March 2006 and March 2007 and constituted 8,234 singleton pregnancies. In 147 (1.8%) cases there was subsequent development of preeclampsia, including 32 that required delivery before 34 weeks (early preeclampsia) and 115 with late preeclampsia. In addition, there were 135 (1.6%) who developed gestational hypertension, 572 (6.9%) who did not develop hypertensive disorders but delivered SGA neonates, and 91 (1.1%) without hypertensive disorders who had spontaneous preterm delivery before 34 weeks. In this study we measured ADAM12 in samples from 128 cases with preeclampsia, including 29 with early disease, 88 with gestational hypertension, 296 with SGA neonates, and 58 with spontaneous preterm delivery before 34 weeks. The selection of the specific samples from each group of pregnancy complications was simply based on availability. There were no significant differences in the demographics between those with and without available samples. Each case with complications was matched for storage time with one control with no pregnancy complications by ensuring that they both were examined on the same day. The investigators were blinded to the results of the questionnaire.
Patients were asked to complete a questionnaire on maternal age, racial origin (white, African American, Indian or Pakistani, Chinese or Japanese, and mixed), cigarette smoking during pregnancy (yes or no), method of conception (spontaneous, use of ovulation drug and in vitro fertilization), medical history (including chronic hypertension, diabetes mellitus, anti-phospholipid syndrome, thrombophilia, human immunodeficiency virus infection, and sickle cell disease), medication (including anti-hypertensive, anti-depressant, anti-epileptic, anti-inflammatory, aspirin, betamimetics, insulin, steroids, thyroxin), parity (parous or nulliparous if no delivery beyond 23 weeks), obstetric history (including previous pregnancy with preeclampsia or spontaneous preterm delivery before 34 weeks), and family history of preeclampsia (mother). The answers given in the questionnaire were confirmed by a doctor, who entered the data into a computer database. The maternal weight and height were measured and the body mass index was calculated in kg/m2.
Data on pregnancy outcome were collected from the hospital maternity records or their general medical practitioners. The obstetric records of all women with preexisting or pregnancy-associated hypertension were examined to determine if the condition was chronic hypertension, preeclampsia, or gestational hypertension. The definitions of preeclampsia and gestational hypertension were those of the International Society for the Study of Hypertension in Pregnancy.22 In gestational hypertension, the diastolic blood pressure should be 90 mm Hg or more on at least two occasions 4 hours apart, developing after 20 weeks of gestation in previously normotensive women in the absence of significant proteinuria, and in preeclampsia, there should be gestational hypertension with proteinuria of 300 mg or more in 24 hours or two readings of at least ++ on dipstick analysis of midstream or catheter urine specimens if no 24-hour collection is available. In preeclampsia superimposed on chronic hypertension, significant proteinuria (as defined above) should develop after 20 weeks of gestation in women with known chronic hypertension (history of hypertension before conception or the presence of hypertension at the booking visit before 20 weeks of gestation in the absence of trophoblastic disease). The newborn was considered to be SGA if the birth weight was less than the 5th percentile after correction for gestation at delivery and sex, maternal racial origin, weight, height, and parity.23
A single serum sample of 25 microliters was used to measure ADAM12 concentration by a heterogeneous time-resolved fluorescent immunoassay, where ADAM12 concentration was directly proportional to the fluorescence measured on time-resolved fluorometer at 615 nm (DELFIA/AutoDELFIA ADAM12 research kit, PerkinElmer Life and Analytical Sciences, Turku, Finland). Fresh aliquots of ADAM12 quality control samples of 77.6, 294.4, and 736.2 pg/mL concentration were measured in duplicate at the beginning and at the end of each run. The mean coefficients of variation were 5.4%, 2.8%, and 3.2%, respectively.
The measured concentration of ADAM12 was log-transformed to make the distribution Gaussian. Multiple regression analysis was then used to determine which of the factors among the maternal characteristics and fetal crown rump length (CRL) were significant predictors of log ADAM12 in the control group, and from the regression model, the value in each case and control was expressed as a multiple of the expected median in the control group (MoM). A box plot of ADAM12 MoM for each outcome group was created. Kruskal-Wallis test and Dunn's procedure were used to determine the significance of differences in the median MoM in each pregnancy complication group to that in the controls.
In each case and control, the measured uterine artery pulsatility index and serum PAPP-A were converted into MoMs after adjustment for gestation, maternal age, racial origin, weight or body mass index, smoking, method of conception, parity, and previous history of preeclampsia as previously described (Poon LC et al. First-trimester maternal serum PAPP-A and preeclampsia. Ultrasound Obstet Gynecol. In press).24 Regression analysis was then used to determine the significance of association between log ADAM12 MoM with either log uterine artery pulsatility index MoM or log PAPP-A MoM in each outcome group.
Logistic regression analysis was used to determine which of the factors among the maternal characteristics, log ADAM12 MoM, log uterine artery pulsatility index MoM, and log PAPP-A MoM had a significant contribution in predicting adverse pregnancy outcome. The performance of screening was determined by receiver operating characteristic curves. The performance of different methods of screening is compared by the areas under the receiver operating characteristics curves.25 The statistical software packages SPSS 15.0 (SPSS Inc., Chicago, IL) and Medcalc (Medcalc Software, Mariakerke, Belgium) were used for all data analyses.
The maternal characteristics of each of the outcome groups are compared in Table 1.
Multiple regression analysis in the control group demonstrated that for log ADAM12, significant independent contributions were provided by fetal CRL, maternal weight, and racial origin (R2=0.272, P<.001; Table 2). In each patient we used this formula to derive the expected log ADAM12 and then expressed the observed value as a MoM of the expected (Fig. 1, Table 3). Cigarette smokers had significantly lower ADAM12 than nonsmokers (Mann-Whitney U test, P=.006), but in the multivariable analysis, smoking did not have a significant contribution in predicting ADAM12 (P=.069).
There was a significant association between log ADAM12 MoM and log PAPP-A MoM (r=0.417, P<.001; Fig. 2), between log ADAM12 MoM and birth weight percentile (r=0.176, P<.001; Fig. 3) and between log PAPP-A MoM and birth weight percentile (r=0.109, P=0.009; Fig. 3), but not between log ADAM12 MoM and log uterine artery pulsatility index MoM (P=.731). Although significant, the correlations shown in Figure 3 are the result of large sample sizes, not strong correlations, as shown by the low r values.
In the SGA group ADAM12 and PAPP-A were lower, and uterine artery pulsatility index was higher than in the controls (Fig. 1, Table 3). There was a significant association between log ADAM12 MoM and log PAPP-A MoM (r=0.420, P<.001; Fig. 2), but not between log ADAM12 MoM and log uterine artery pulsatility index MoM (P=.713). Logistic regression analysis demonstrated that significant contributions for the detection of SGA were provided from maternal factors, ADAM12, and PAPP-A (R2=0.232, P<.001; Table 4) but not uterine artery pulsatility index (P=.070).
The areas under the receiver operating characteristics curves and detection rates of SGA for different false-positive rates in screening by maternal factors, serum ADAM12, serum PAPP-A, uterine artery pulsatility index, and by their combinations are given in Tables 5 and 6. In the prediction of SGA, the areas under the receiver operating characteristics curves were significantly higher in screening by history with ADAM12 and PAPP-A than by history alone (P<.001).
In the preeclampsia group, compared with the controls, there were no significant differences in ADAM12, but PAPP-A was lower, and uterine artery pulsatility index was higher (Fig. 1, Table 3). There was a significant association between log ADAM12 MoM and log PAPP-A MoM (r=0.412, P<.001) but not between log ADAM12 MoM and log uterine artery pulsatility index MoM (P=.079). There was no significant association between log ADAM12 MoM and either gestation at delivery (P=.474) or birth weight percentile (P=.097). There were no significant differences in median ADAM12 MoM between the group of preeclampsia with SGA (n=42) and the group of preeclampsia without SGA (n=86) (0.974 MoM compared with 0.953 MoM, P=.749) and between the group of preeclampsia resulting in delivery before 34 weeks (n=29) and the group delivering at or after 34 wks (n=99) (1.015 MoM compared with 0.946 MoM, P=.871).
In the gestational hypertension group, compared with the controls, there were no significant differences in ADAM12, PAPP-A, or uterine artery pulsatility index (Fig. 1, Table 3). In the preterm delivery group, compared with the controls, there were no significant differences in ADAM12, PAPP-A, or uterine artery pulsatility index (Fig. 1, Table 3).
The findings of this study demonstrate that the maternal serum ADAM12 concentration at 11 0/7 to 13 6/7 weeks of gestation in normal pregnancies increased with fetal CRL and therefore gestational age, decreased with maternal weight, and was higher in African-American than in white women. Consequently, the measured concentration of ADAM12 must be adjusted for these variables before comparing results with pathologic pregnancies. The finding is not surprising, because there was a good correlation between ADAM12 and PAPP-A, which has been shown in a previous study involving 96,803 pregnancies to also increase with CRL, decrease with maternal weight, and to be higher in African-American than in white women.24 Another variable that affects the concentration of PAPP-A is cigarette smoking, but in the case of ADAM12—although in the univariable analysis, the levels in smokers were lower than in nonsmokers—in the multivariable analysis the contribution of smoking was not significant. The extent to which this is a mere reflection of the small number of cases examined in this study by comparison with the study of PAPP-A24 remains to be determined.
In pregnancies developing preeclampsia or gestational hypertension, the maternal serum ADAM12 concentration at 11 0/7 to 13 6/7 weeks of gestation was not significantly different from normotensive pregnancies. Furthermore, there was no significant association between ADAM12 and the severity of preeclampsia, irrespective of whether this was defined by the gestation at which iatrogenic delivery was carried out or the coincidence of preeclampsia with SGA. The findings of our study contradict the reported results of two previous studies that in pregnancies developing preeclampsia the first-trimester maternal serum ADAM12 concentration is reduced6,7 and is particularly low in those cases requiring early delivery7 and in those with coincidence of preeclampsia with SGA.6 A likely explanation for this apparent contradiction is that in both of these studies the level of ADAM12 was adjusted only for gestational age.6,7 Reanalysis of our data without adjustment for maternal weight and racial origin also demonstrated that the maternal serum ADAM12 in pregnancies developing preeclampsia was significantly lower than controls (0.927 MoM compared with 1.039 MoM, P=.016). Therefore, the conclusion that the development of preeclampsia is associated with low levels of ADAM12 may be a simple reflection of the association between the development of preeclampsia and increasing maternal weight.26
In normal pregnancies there is a correlation between birth weight percentile and the maternal serum concentration of ADAM12 and PAPP-A at 11 0/7 to 13 6/7 weeks of gestation, providing further evidence for the possible contribution of these placental products in the control of fetal growth. The levels of ADAM12 and PAPP-A during the first trimester were low in women who subsequently delivered small neonates and high in those delivering large neonates. However, the performance of screening for SGA using ADAM12 was poor because low levels below the 5th percentile were observed only in about 15% of the SGA pregnancies. There was a good correlation between the maternal serum levels of ADAM12 and PAPP-A, and consequently the additional contribution of PAPP-A in the prediction of SGA was only about 2%. Similarly, although the uterine artery pulsatility index at 11 0/7 to 13 6/7 weeks in the SGA pregnancies was significantly increased, this measurement did not improve the prediction of SGA provided by maternal demographic characteristics and medical history alone.
In pregnancies resulting in spontaneous preterm delivery, the maternal serum ADAM12 concentration at 11 0/7 to 13 6/7 weeks of gestation was not significantly different from pregnancies delivering at term. These findings are not surprising, because there is only a weak association between impaired placentation and spontaneous preterm delivery. Histologic studies reported that in patients with spontaneous preterm delivery, there is failure of the physiologic transformation of the maternal spiral arteries, but to a substantially lower extent than in cases developing preeclampsia.27–29 Doppler studies of the uterine arteries have demonstrated increased pulsatility index in association with preterm delivery, but this relationship was mainly observed in pregnancies undergoing iatrogenic delivery for preeclampsia and SGA rather than in cases of spontaneous preterm delivery.30 There is evidence that in pregnancies resulting in spontaneous preterm delivery, the maternal serum concentration of PAPP-A at 11 0/7 to 13 6/7 weeks is reduced, but PAPP-A below the 5th percentile was observed in only 10% of preterm deliveries.10
This was a case-control study in which ADAM12 was not measured in all cases from the base cohort but in those with available samples. However, this potential bias is unlikely to be important, because there were no significant differences in the demographics between those with and without available samples.
In conclusion, at 11 0/7 to 13 6/7 weeks of gestation, there is a good correlation between the maternal serum ADAM12 and PAPP-A concentration, and in pregnancies delivering SGA neonates, the levels of both metabolites are reduced. However, measurement of ADAM12 does not provide useful prediction of SGA. In pregnancies complicated by preeclampsia, gestational hypertension, and spontaneous preterm delivery, the levels of ADAM12 are not significantly different from normal.
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© 2008 The American College of Obstetricians and Gynecologists
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