In order to identify features associated with an increased risk of tra
nsmission of HIV from seropositive women to their offspring, 70 childr
en of 58 HIV seropositive mothers were studied. Fifty-six children wer
e followed prospectively from pregnancy; in 14 identified after the pu
erperium, obstetric notes were reviewed and stored serum was tested. T
welve infants of 10 mothers were HIV infected. Risk of transmission wa
s increased in the first year after seroconversion; 5/9 infants born a
t this time were infected compared with 7/61 born subsequently (P<0.00
1). Progression to stage IV in transmitters was more likely, occurring
in the mothers of 9 infected children at a median of 3 years (range 0
.5-6.5) and in mothers of 19 non-infected children at a median of 5 ye
ars (range 1-7) (P = 0.032). Maternal CD4+ counts <400 x 10(6)/l were
found in 7/12 transmitting and 7/49 non-transmitting pregnancies (P<0.
01). Differences in HIV antigenaemia did not reach significance. These
factors may influence the counselling of mothers regarding their chil
d's and their own prognosis.