A total of 520
689 parous women who delivered singleton infants between 1985 and 1997 were recorded on our database. The final study population included 456
889 women whose records contained complete data on interpregnancy interval and adverse maternal outcomes. There were no significant differences between the women excluded because of incomplete data and those with complete data with regard to maternal age, parity, education, and marital status.
The median interpregnancy interval was 27 months. Short (<6 months) and long (>59 months) intervals between pregnancies were observed for 2.8% and 19.5% of women, respectively. Almost a third of the women had an interpregnancy interval of less than 18 months.
Table shows the characteristics of the mothers at the index pregnancy according to interpregnancy interval. Younger maternal age, history of miscarriage, fetal death and early neonatal death, lower rate of previous caesarean delivery, later start of prenatal care, lower number of prenatal visits, and lower body mass index before pregnancy were associated with short intervals between pregnancies. Conversely, women with a long interpregnancy interval were more likely to be older, with greater body mass index before pregnancy, and with a history of chronic hypertension. Start of prenatal care and number of prenatal visits correlated with interpregnancy interval: the shorter the interval, the later care started and the lower the number of prenatal visits. There were no obvious differences among the interpregnancy interval groups with regard to number of previous deliveries, mother's education, marital status, and cigarette smoking during pregnancy.
Table 1 Distribution of sociodemographic and obstetric characteristics according to interpregnancy interval in cohort of 456889 Latin American and Caribbean women delivering singleton infants, 1985-97. Figures are percentage of women
Women with short interpregnancy intervals had the highest rates of third trimester bleeding, premature rupture of membranes, puerperal endometritis, anaemia, and maternal death (table ). There were 220 maternal deaths in the study population The rates of pre-eclampsia, eclampsia, and gestational diabetes mellitus were highest among women with intervals longer than 59 months. A slight increase in the rates of third trimester bleeding and maternal death was also seen in women with this interpregnancy interval.
Table 2 Rates of adverse maternal outcomes according to interpregnancy interval in cohort of 456889 Latin American and Caribbean parous women delivering singleton infants, 1985-97. Figures are percentage of women
Table shows the results of multiple logistic regression analysis of the relation of interpregnancy intervals to adverse maternal outcomes. Compared with mothers with interpregnancy intervals of 18 to 23 months, mothers with intervals shorter than 6 months had about a 70% increased risk of third trimester bleeding and premature rupture of membranes and a 30% increased risk of anaemia and puerperal endometritis. Moreover, a short interval between pregnancies was associated with a significantly greater risk of maternal death (adjusted odds ratio 2.54; 95% confidence interval 1.22 to 5.38). When interpregnancy intervals were dichotomised to shorter than 6 months versus 6 months or more, women with short intervals between pregnancies were significantly more likely to die than women conceiving at or after 6 months (2.04; 1.13 to 3.78). On the other hand, women with interpregnancy intervals of 60 months or more were 1.8 times more likely than women with intervals of 18 to 23 months to develop pre-eclampsia and eclampsia. We found no significant differences in the effect of interpregnancy interval on gestational diabetes mellitus, and no relation between the interval and the risk of postpartum haemorrhage.
Table 3 Adjusted relative risk (95% confidence interval) for adverse maternal outcomes according to interpregnancy interval in cohort of 456889 Latin American and Caribbean parous women delivering singleton infants, 1985-97*