Counsel women about increased risks associated with pregnancy at later age, study recommends

BMJ 2007; 334 doi: (Published 22 February 2007) Cite this as: BMJ 2007;334:389
  1. Roger Dobson
  1. Abergavenny

    A study that looked at data on more than eight million live births in the United States shows that the most common complications of pregnancy facing mothers aged ≥45 years are raised blood pressure, preterm birth, and excessive bleeding during labour.

    Labour is also more likely to be prolonged or dysfunctional in this age group, and the risk of breech or caesarean delivery is higher, says the study, which was published online on 8 February in Human Reproduction (, doi: 10.1093/humrep/del522).

    “This analysis demonstrates the substantial increased risks of pregnancy complications that accompany advancing maternal age. These risks should be considered when counselling older women during infertility treatment and in their subsequent antenatal management,” says the report.

    The number of older mothers having babies is growing in many countries. In the United States, between 1980 and 2004 the proportion of first births that were in women aged ≥30 tripled (from 8.6% to 25.4%). The proportion of first births that were in women aged ≥35 grew sixfold (1.3% to 8.3%), and that in women aged ≥40 grew 15-fold (0.1% to 1.5%).

    The report says that the shift in the age of child bearing is partly due to the greater availability and widespread use of fertility treatments.

    The study analysed 8 079 996 live births between 1995 and 2000 in women aged 30 to 54. The results show that mean birth weight decreased with advancing maternal age, while the proportion of low birthweight babies (<2500 g) and very low birthweight babies (<1500 g) increased. Among women aged ≥45 the adjusted odds ratio for having a baby with a very low birth weight was 1.7 (P<0.001). Also, the proportion of term births (at 37 weeks or later) was lower in this age group (16%) than in the group of women aged 30 to 34 years (18%).

    The study looked at the odds ratios of various risks of pregnancy by age and parity. Among the highest adjusted odds ratios in women aged ≥45 when compared with women aged 30–34 were those for chronic hypertension (odds ratio 3.7 (3.1 to 4.4) in primiparous women and 4.9 (4.5 to 5.4) in multiparous women), hypertension during pregnancy (1.6 (1.4 to 1.8) and 2.1 (2.0 to 2.3), and birth at less than 32 weeks' gestation (2.1 (1.8 to 2.5) and 1.8 (1.6 to 2.0)).

    The analysis also found that the risk of infant death grew with advancing age in multiparous women, which the authors say may be partly linked to the rising prevalence of obesity. The odds ratio for infant death in women aged ≥45, adjusted for congenital anomalies and gestational age, was 1.6 (1.3 to 1.9). The report says that 29% of US women aged 20-39 and 37% of those aged 40-59 are obese (body mass index >30).

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