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. 2021 Aug;41(9):1074-1079.
doi: 10.1002/pd.5997. Epub 2021 Jun 27.

Twin chorionicity and zygosity both vary with maternal age

Amanda Yeaton-Massey  1 , Teresa N Sparks  1 , Mary E Norton  1 , Laura Jelliffe-Pawlowski  2   3 , Robert J Currier  4
Affiliations

Twin chorionicity and zygosity both vary with maternal age

Amanda Yeaton-Massey et al. Prenat Diagn. 2021 Aug.

Abstract

Objective: To determine the ratio of dichorionic (DC) to monochorionic (MC) twins by maternal age.

Methods: We reviewed all twin pregnancies undergoing first trimester screening (FTS) with nuchal translucency from April 2009 to December 2012 with sonographic determination of chorionicity. Cases were linked to newborn screening (NBS) results and zygosity estimated based on rates of fetal sex discordance. The ratio of DC to MC placentation by maternal age was calculated.

Results: We identified 11,351 twin pregnancies with FTS and documented chorionicity. Among these, 7,861 (64.2%) had linked data on FTS and NBS to allow estimation of zygosity based on neonatal sex. Of these, 1,464 (18.6%) were MC and 6,406 (81.4%) DC. The MC twin rate remained constant while the DC twin rate increased with maternal age until 40y. At < 20y, 55% of twin pregnancies were monozygotic (MZ), as compared to 29% at ≥ 40y. Of MZ twins, 38% were DC at < 20y, while 53% were DC at ≥ 40y.

Conclusions: Our data suggest a relationship of both zygosity and chorionicity with maternal age. DZ twinning increased with maternal age, while among MZ twins, the proportion that were DC also increased with maternal age.

Keywords: chorionicity; maternal age; twins; zygosity.

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Conflict of interest statement

Conflict of Interest Statement: The authors report no conflicts of interest

Figures

Figure 1:
Figure 1:. Zygosity and chorionicity for twin pregnancies with known chorionicity and sex
Flow diagram showing number (N) of pregnancies stratified by zygosity and chorionicity for no ovum donor and ovum donor. Complete data includes linkage to two newborn screen results and sex for both babies.
Figure 2:
Figure 2:. Rates of twin pregnancy by zygosity and chorionicity by maternal age
Graph showing rates of twin pregnancy by zygosity and chorionicity (Y-axis) by maternal age (X-axis).
See this image and copyright information in PMC

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