Effects of a first miscarriage on future pregnancies

Miscarriage (or spontaneous pregnancy loss) is defined as pregnancy loss before 24 completed weeks of gestation. There is a 20% (one in five) risk of pregnancies ending in a miscarriage in the first three months and one in 100 women have recurrent miscarriages (three or more successive miscarriages).

Most preceding research has focussed on the risk of another miscarriage recurring after a woman has had an initial miscarriage. This is one of the few studies examining the obstetric and perinatal outcomes in subsequent pregnancies after 24 weeks of gestation.

In this study, researchers from the University of Aberdeen compared three different groups of women: Women who had a miscarriage in their first pregnancy (1,561 women, average gestation at miscarriage 9 weeks) and were pregnant for a second time, women who had a livebirth in their first pregnancy and were pregnant for a second time (10, 549 women), and women pregnant for the first time (21, 118 women).

Data about these women (including their socio-demographic details) were obtained from the Aberdeen Maternity and Neonatal Databank between 1986 and 2000.

The key findings were that women who had a miscarriage in their first pregnancy had a higher risk of adverse outcomes in their next pregnancy compared both to women who had a successful first pregnancy and women pregnant for the first time.

Compared with women with a successful first pregnancy, women with a previous miscarriage were 3.3 times more likely to have pre-eclampsia, 1.7 times more likely to have a threatened miscarriage, and 1.3 times more likely to have bleeding after 24 weeks. They were 2.2 times more likely to have labour induced, 5.9 times more likely to have an instrumental vaginal delivery, and 1.5 times more likely to have a manual removal of placenta. Preterm birth after 34 weeks gestation was 1.6 times more common, and low birthweight (<2500g) was 1.6 times more common. Compared to women pregnant for the first time, women with a previous miscarriage were 1.5 times more likely to have a threatened miscarriage, 1.3 times more likely to have an induced labour, 1.4 times more likely to have a postpartum haemorrhage, and 1.5 times more likely to have a preterm birth after 34 weeks (2.8 times higher if the first miscarriage was after 12 weeks). What this means is that women pregnant for the second time after a previous miscarriage generally behave as if they were having a first pregnancy, except for the increased risks of threatened miscarriage, induction of labour, preterm birth and postpartum haemorrhage. Dr Sohinee Bhattacharya, co-researcher from the Dugald Baird Centre for Research on Women's Health at the University of Aberdeen and Aberdeen Maternity Hospital, said "This is the first study of its kind to assess the impact of an initial miscarriage on the next ongoing pregnancy. Previous work has focussed on the consequences of three or more miscarriages (recurrent miscarriage), although for most women, a single miscarriage is far more likely. "Using a large Scottish population-based dataset, we analysed pregnancy records of more than 32,000 women. A single initial miscarriage increased the risks of pregnancy complications in the next continuing pregnancy compared to women who had a successful first pregnancy. While for most women these risks are small, increased obstetric surveillance should not be restricted only to women with multiple miscarriages." Professor Philip Steer, BJOG editor-in-chief said, "The findings from this research are helpful to healthcare professionals caring for pregnant women. They provide us with an idea of the complications that may arise as a result of a previous miscarriage. This will help doctors in the management of the subsequent pregnancy. One factor not assessed in this study was the interval between the miscarriage and the next pregnancy. This is important because many previous studies have shown that an interval of less than six months between the miscarriage and the next pregnancy substantially increases the risk of pregnancy complications, and the risk does not reach a minimum until 18 months to two years. Thus, women wishing to minimise the risk in the next pregnancy after a miscarriage should ideally wait for 18 months before trying to conceive again." Source: Royal College of Obstetricians and Gynaecologists, UK

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