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The incidence of chromosomal abnormalities in twin pregnancies is not well-studied. In this retrospective study, we investigated the frequency of chromosomal abnormalities in twin pregnancies and compared the incidence of chromosomal abnormalities in dichorionic diamniotic (DD) and monochorionic diamniotic (MD) twins. We used data from 57 clinical facilities across Japan. Twin pregnancies of more than 12 weeks of gestation managed between January 2016 and December 2018 were included in the study. A total of 2899 and 1908 cases of DD and MD twins, respectively, were reported, and the incidence of chromosomal abnormalities in one or both fetuses was 0.9% (25/2899) and 0.2% (4/1908) in each group (p = 0.004). In this study, the most common chromosomal abnormality was trisomy 21 (51.7% [15/29]), followed by trisomy 18 (13.8% [4/29]) and trisomy 13 (6.9% [2/29]). The incidence of trisomy 21 in MD twins was lower than that in DD twins (0.05% vs. 0.5%, p = 0.007). Trisomy 21 was less common in MD twins, even when compared with the expected incidence in singletons (0.05% vs. 0.3%, RR 0.15 [95% CI 0.04–0.68]). The risk of chromosomal abnormality decreases in twin pregnancies, especially in MD twins.

To assess whether adiponectin gene (ADIPOQ) polymorphism is associated with intrauterine fetal growth and cord blood adiponectin, we investigated eight single-nucleotide polymorphisms (SNPs; rs182052, rs710445, rs16861205, rs12495941, rs1501299, rs3774261, rs2082940 and rs266729) in ADIPOQ and birth weight and cord blood adiponectin in 526 healthy neonates. We found that the neonates carrying the G allele of rs266729 had a significantly greater birth weight s.d. score than those homozygous for the C allele (CC: -0.06±0.75 versus CG: 0.20±0.64 versus GG: 0.07±0.78; P=1.65 × 10(-3), adjusted P=9.90 × 10(-3)). However, this difference was not significant after adjustment for cord blood adiponectin (P=0.04, adjusted P=0.26). The rs266729 SNP was strongly associated with cord blood adiponectin; neonates with rs266729 GG had the highest adiponectin (CC: 34.1±20.2 versus CG: 44.3±26.1 versus GG: 54.1±36.7 μg ml(-1), P=2.80 × 10(-9), adjusted P=1.68 × 10(-8)). This association remained after adjustment for birth weight s.d. score (P=6.63 × 10(-8), adjusted P=3.98 × 10(-7)). Our results suggest that the influence of the rs266729 SNP in ADIPOQ on birth weight may be dependent on circulating adiponectin.

The Leiden mutation in the coagulation factor V (F5) gene associated with preeclampsia in Caucasians has not been found in Japanese populations. We examined the association of 20 missense polymorphisms in the F5 gene in 133 pregnant Japanese women with preeclampsia and in 224 unrelated, healthy, pregnant Japanese women. Among nine polymorphisms identified in the subjects, the M385T and R485K polymorphisms were associated with preeclampsia (P = 0.05 and P = 0.02, respectively). Haplotype analysis indicated that the R485K polymorphism is truly associated with preeclampsia, whereas the association of the M385T polymorphism is due to linkage disequilibrium. Taken together with reports that the R485 allele yields poor factor V function in comparison with that of the K485 allele and that the F5 Leiden mutation is associated with preeclampsia in Caucasian populations, the findings of the present study suggest that the F5 gene is associated with preeclampsia in pregnant Japanese women.

Preeclampsia is associated with thrombosis of the intervillous or spiral artery. A deletion/insertion polymorphism (4G or 5G) in the promoter of the plasminogen activator inhibitor type 1 (PAI-1) gene is suggested to be involved in regulating the synthesis of the inhibitor, 4G allele, being associated with the enhanced gene expression and plasma PAI-1 levels. We assessed the association between preeclampsia and the 4G/5G polymorphism of the PAI-1 gene in 115 preeclamptic patients, 210 pregnant controls, and 298 healthy volunteer controls. The frequency of the homozygotes for the 4G allele was significantly higher in the patients than in the control pregnant women (P = 0.04) or in the healthy volunteers (P = 0.02). The 4G allele frequency was also significantly higher in the patients than in the control group of pregnant women (P = 0.03) and in the healthy volunteers (P = 0.02). These results suggest that the presence of the 4G/4G genotype of the PAI-1 gene is one of the risk factors for preeclampsia.