Gestational age determination and prevention of HIV perinatal transmission

To compare different methods of gestational age (GA) measurement for ensuring effective zidovudine (ZDV) prophylaxis to prevent mother-to-child transmission of HIV.

For 1398 HIV-infected women enrolled in a perinatal prevention trial, gestation durations were calculated based on GA estimated using ultrasound (US), date of last menstruation period (LMP), first fundal height (FH(1)), and a specific algorithm was developed to provide a "reference" GA. The performance of each GA estimate was evaluated by the percentage of women who would have received > or =8 weeks ZDV, if prophylaxis was initiated at 28 weeks.

The performances of the algorithm, US, LMP, and FH(1) were 95.5%, 94.8%, 88.4%, and 83.7%, respectively. US and FH(1) were significantly better when estimated before and after 24 weeks, respectively.

In situations where no US is available and LMP is not or imprecisely known, FH(1) can be used after 24 weeks to schedule ZDV initiation date.