Twenty studies were included in the review (one trial, 11 prospective cohorts, seven retrospective cohorts and one case control study). Twelve cohort studies were included in the meta-analysis (n=2,502 participants). Study quality was reported as low to medium risk of bias.
Compared with no such care, preconception care was associated with a statistically significantly lower rate of congenital malformation (RR 0.25, 95% CI 0.15 to 0.42, NNT=17; 11 studies), pre-term delivery (RR 0.70, 95% CI 0.55 to 0.90, NNT=8; four studies) and perinatal mortality (RR 0.35, 95% CI 0.15 to 0.82, NNT=32; five studies). There was no evidence of statistical heterogeneity.
A statistically significant difference in the level of hbA1C favoured preconception care (OR 2.43%, 95% CI 2.27 to 2.58; four studies). There was a high level of statistical heterogeneity (I2=97%).
There was evidence that preconception care statistically significantly reduced the mean gestational age at the time of the first antenatal visit (OR -1.32 weeks, 95% CI -1.40 to -1.23; three studies). There was significant statistical heterogeneity (I2=85%).
There was evidence of a reduction in maternal hyperglycemia with no preconception care (RR 1.51, 95% CI 1.15 to 1.99; two trials). This result was associated with significant heterogeneity (I2=85%).
There was no statistical difference in risks of spontaneous abortions, pre-eclampsia, caesarean delivery, macrosomia, neonatal hypoglycaemia, respiratory distress syndrome and small for gestational age.