Table 5

Congenital malformations in twins according to time to pregnancy (TTP) and infertility treatment

Twins born of infertile couples who conceived naturally (TTP>12 months) (n=100)Twins born of infertile couples who received infertility treatment (n=1690)
Hazard ratio (95% CI)*Hazard ratio (95% CI)*
MalformationsNo (%) twins born of fertile couples (TTP≤12 months) (n=1366)No (%)CrudeAdjustedNo (%)CrudeAdjusted
All102 (7.5)11 (11.0)1.461.53 (0.80 to 2.91)107 (6.3)0.850.90 (0.67 to 1.21)
Nervous system2 (0.1)0--7 (0.4)2.902.83 (0.60 to 13.41)
Eye, ear, face, and neck5 (0.4)1 (1.0)2.692.69 (0.33 to 22.15)3 (0.2)0.490.45 (0.10 to 2.04)
Circulatory system31 (2.3)3 (3.0)1.301.56 (0.49 to 4.97)25 (1.5)0.650.73 (0.42 to 1.29)
Respiratory system4 (0.3)0--8 (0.5)1.621.48 (0.42 to 5.18)
Cleft lip/palate7 (0.5)0--2 (0.1)0.230.25 (0.06 to 1.05)
Digestive system10 (0.7)1 (1.0)1.351.30 (0.15 to 11.07)7 (0.4)0.570.56 (0.19 to 1.62)
Genital organs11 (0.8)2 (2.0)2.433.31 (0.68 to 16.07)11 (0.7)0.821.12 (0.45 to 2.80)
Urinary system5 (0.4)3 (3.0)8.2111.50 (1.05 to 126.02)7 (0.4)1.131.57 (0.30 to 8.26)
Musculoskeletal system37 (2.7)3 (3.0)1.091.06 (0.33 to 3.41)50 (3.0)1.101.13 (0.71 to 1.78)
Other malformations12 (0.9)1 (1.0)1.141.24 (0.18 to 8.62)9 (0.5)0.600.64 (0.28 to 1.47)
Chromosomal abnormalities3 (0.2)0--2 (0.1)0.540.41 (0.05 to 3.15)
  • * Cox regression; reference group=twins born of fertile couples.

  • † Adjusted for maternal age at conception, pre-pregnancy body mass index, smoking, alcohol intake, coffee consumption, and occupational status.

  • ‡ Children with two or more malformations counted once for all congenital malformations but counted for each malformation in relevant subgroup.