Early first-trimester free β-hCG and PAPP-A serum distributions in monochorionic and dichorionic twins

The impact of preimplantation genetic testing on first- and second-trimester maternal serum analyte levels

OBJECTIVE

To determine whether preimplantation genetic testing (PGT) is associated with a change in maternal serum analyte levels in pregnancies conceived via in vitro fertilization (IVF).

METHODS

Retrospective cohort of singleton and twin IVF pregnancies with available first- or second-trimester serum analyte data from 01/2014 to 09/2019. Multiple of the median (MoM) values for free β-human chorionic gonadotropin (β-hCG), pregnancy-associated plasma protein A (PAPP-A), alpha-fetoprotein (AFP), inhibin A, and unconjugated estriol, were compared between two groups: pregnancies conceived after transfer of PGT screened euploid embryos vs. those conceived after transfer of untested embryos. Multiple linear regression of log MoM values with F test was performed to adjust for potential confounders.

RESULTS

Nine hundred and sixty-two singleton and 165 twin IVF pregnancies with serum analyte data available for analysis were included. PGT was associated with a higher median first- and second-trimester AFP compared to no PGT in singletons (1.23 MoM vs. 1.13 MoM; parameter estimate [PE] 1.08, 95% CI 1.00-1.17, p= .04, and 1.21 MoM vs. 1.07 MoM; PE 1.07, 95% CI 1.01-1.13, p= .01, respectively). PGT was also associated with a lower median PAPP-A compared to no PGT in twins (0.75 MoM vs. 1.18 MoM, PE 0.74, 95% CI 0.60-0.92, p= .006).

CONCLUSIONS

Our data suggest that PGT is associated with higher maternal serum levels of second-trimester AFP in singleton and lower levels of first-trimester PAPP-A in twin pregnancies conceived via IVF.

Screening and Invasive Testing in Twins

Prenatal screening and testing for trisomy 21 in twin pregnancies poses a number of challenges: the exact estimate of the a priori risk of trisomy 21, the choice of prenatal screening test and/or invasive techniques to employ for the diagnosis and the impact of the result on the options of treatment in case of discordant results within a twin pair or among multiples. These different aspects are discussed below while recognizing that many issues remain unresolved.

Down syndrome screening in assisted conception twins: an iatrogenic medical challenge

OBJECTIVE

The objective of this study was to provide a critical analysis of the impact of assisted conception on prenatal screening for Down syndrome (DS) in twin pregnancies and the value of various screening modalities for early detection of anomalies.

METHODS

The literature was searched using PubMed and the Cochrane Library focusing on prenatal screening and antenatal care of assisted-conception twin pregnancies.

RESULTS

Serum screening alone is of limited value in detecting aneuploid twins, because the unaffected cotwin can "mask" the abnormal serum results of an affected one. In addition, this test can designate the pregnancy as at high risk but not identify the affected fetus. Nuchal translucency (NT) screening is the best available modality and a highly effective screening method for twin pregnancies. Among twins, NT alone has a 69% DS detection rate, first-trimester combined NT and serum biochemistry has a 72% DS detection rate, and an integrated screen will have an 80% DS detection rate at a 5% FPR. The data in the literature concerning the effect of assisted conception on maternal serum screening markers in twin pregnancies are scarce.

CONCLUSIONS

Down syndrome screening in assisted-conception twins presents clinical and technical challenges. Therefore, assisted-conception twins need close monitoring from conception to delivery, by a practitioner familiar with the available screening modalities and their relative accuracy.

Analysis of three different strategies in prenatal screening for Down's syndrome in twin pregnancies

OBJECTIVES

To compare the performance of three different strategies in prenatal screening for Down's syndrome in twins [nuchal translucency, the combined test, the combined test + ductus venosus pulsatility index (DVPI)].

METHODS

We included 277 twin pregnancies with two cases of trisomy 21 (both dichorionic). We performed a computer simulation of Down's syndrome NT screening, combined test screening and the combined test with the addition of DVPI screening using the commercialized software SsdwLab6. The strategies were compared using the area under the receiver operating characteristic curve.

RESULTS

NT screening false-positive rate (FPR) was 10.9% (95% CI: 8.3-13.5). The combined test FPR was 6.2% (95% CI: 4.1-8.2%) and the combined test plus DVPI was 6% (95% CI: 4-8). FPR was higher in advanced maternal age patients. Detection rate was 100% in all cases. The area under the curve was 0.987 (95% CI: 0.972-0.994) in NT screening; 0.987 (95% CI: 0.978-0.997) in the combined test and 0.983 (95% CI: 0.977-0.996) in the combined test + DVPI.

CONCLUSIONS

Down's syndrome screening is feasible in twins with low FPR. The results of this study are similar to the results achieved in singletons. The combined test appears to be the most effective. The addition of DVIP does not significantly improve the prenatal screening for trisomy 21.

Prenatal diagnosis in twin gestations

Twin gestations face an increased risk of structural abnormalities compared with singleton gestations, as well as an increased risk of aneuploidy. Accordingly, there is a need for accurate prenatal diagnosis of fetal genetic disorders and structural anomalies in twin gestations. Given the increased risk of congenital anomalies, a detailed sonographic survey of fetal anatomy is recommended in the early second trimester of twin gestations. In addition, fetal echocardiography should be considered in monochorionic twin gestations and in dichorionic twin pregnancies conceived using assisted reproductive technologies given the increased risk of congenital heart disease in these populations. Although first- and second-trimester aneuploidy screening in twin gestations is available, screening is less accurate than in singleton gestations. Invasive prenatal diagnosis in twin pregnancies is associated with a risk of pregnancy loss that is higher than the baseline risk of loss among twin gestations. Precise procedure-related loss rates in twin gestations undergoing chorionic villus sampling or amniocentesis, however, remain unclear because of methodological differences between published studies investigating diagnostic procedures in twins.

Are first-trimester screening markers altered in assisted reproductive technologies pregnancies?

PURPOSE OF REVIEW

To review the current literature on first-trimester screening with respect to specific issues for assisted reproductive technologies (ARTs) singleton and twin pregnancies.

RECENT FINDINGS

A number of different first-trimester sonographic and biochemical markers have been validated in first-trimester screening for trisomy 21. Among sonographic markers, measurement of fetal nuchal translucency is the most investigated and least affected screening method in ART pregnancies, achieving comparable results in singletons and twins compared with spontaneous conceptions. The small deviation of nuchal translucency thickness observed in ART singletons did not influence overall screening performance, including the number of false-positive results. First-trimester maternal serum free β-human chorionic gonadotropin and pregnancy-associated plasma protein-A levels are more obviously altered in assisted conceptions and carry the risk of higher false-positive rates if not adjusted accordingly. The reason behind the alterations is currently not quite explored, but might be attributed to infertility and a higher incidence of placental disorders rather than to the use of ART. In twin pregnancies, chorionicity is an important confounding variable with evident impact on nuchal translucency measurements and maternal biochemistry, but both issues have not been sufficiently investigated in ART twins so far.

SUMMARY

First-trimester measurement of fetal nuchal translucency in singleton and twin gestations is associated with similar screening results when compared with spontaneous conception. Adjustments for the mode of conception are required if maternal serum biochemistry is included in the screening algorithm. Further studies on assisted conception twins are essential to permit more conclusive results on this issue.

A reassessment of biochemical marker distributions in trisomy 21-affected and unaffected twin pregnancies in the first trimester

OBJECTIVE

To estimate the difference between levels of the two biochemical markers pregnancy-associated plasma protein-A (PAPP-A) and maternal serum free β-human chorionic gonadotropin (free β-hCG) in twin pregnancies relative to singleton pregnancies and establish an improved screening procedure for chromosomal abnormalities such as trisomy 21 in twin pregnancies.

METHODS

4843 unaffected and 47 trisomy 21-affected twin pregnancies were included in the study. Chorionicity-specific medians were generated for PAPP-A and free β-hCG from gestational ages 8 to 14 weeks. Multiple of the median values for each of the biochemical markers were calculated. Detection rates and false-positive rates were estimated for screening tests incorporating nuchal translucency and maternal age, with and without biochemistry.

RESULTS

Medians for the two biochemical markers for monochorionic and dichorionic twins in unaffected pregnancies show a gestational age-specific increase relative to singleton medians. Allowing for gestation and chorionicity, twin pregnancies affected with trisomy 21 had higher levels of free β-hCG and lower levels of PAPP-A. Adding biochemistry into the risk assessment using a fixed risk cut-off of 1 in 100 increased the detection rate for fetal trisomy 21 in dizygotic twin pregnancies from 78 to 90%, and decreased the false-positive rate from 8.0 to 5.9%.

CONCLUSION

Generation of chorionicity-specific medians for the biochemical markers and their use in risk assessment can improve the performance of first-trimester screening for chromosomal abnormalities in twins to a level comparable with that in singleton pregnancies.

First trimester maternal serum ADAM12s levels in twin pregnancies

BACKGROUND

A disintegrin and metalloprotease 12s (ADAM12s) is a potential first trimester serum marker for fetal trisomy and adverse pregnancy outcome in singletons. In this study, ADAM12s levels in first trimester serum of uncomplicated and complicated twins were evaluated.

METHODS

ADAM12s was studied in maternal serum of 215 twin pregnancies, collected between 2004 and 2008. ADAM12s was measured 'blind to outcome' using AutoDelfia (PerkinElmer, Turku, Finland). As a reference, data from 2423 singletons were used.

RESULTS

The median ADAM12s level was increased in euploid twins [1.61 multiples of the median (MoM); n = 209] compared with singletons. The median ADAM12s MoM was significantly lower in monochorionic (1.36 MoM; n = 41) compared with dichorionic twins (1.67 MoM; n = 168) (Mann-Whitney U test, p = 0.005). Trisomy 21 was identified in two pregnancies. Median ADAM12s MoM in twins complicated by hypertensive disorders (1.77 MoM, n = 35) or small for gestational age fetus (1.54 MoM; n = 24) was not significantly different from uncomplicated twins (1.64 MoM; n = 134).

CONCLUSION

Median ADAM12s MoM in euploid twins was increased compared with singletons. Monochorionic had significantly lower median ADAM12s MoM than dichorionic twins. Median ADAM12s MoMs were not significantly different in twins complicated by hypertensive disorders or small for gestational age fetus compared with uncomplicated twins.