reptilefacts:

Boa constrictors are ovoviviparous - the embryos develop inside eggs that the mother retains until giving birth to live young. The gestation period, which is counted from the post ovulation shed, is approximately 100–120 days. When the female gives birth to the young they average 15-20in (38–51cm) in length. The litter size varies between females, but can be between 10 and 65 young with an average of 25, although some of the young may be stillborn or non-fertilised eggs known as “slugs”.

This photo shows the new born boas just before they pop through the amniotic sack. Once they’ve gotten out of the sack, the young fend for themselves. When in captivity it’s best to immediately separate the young from the mother in case she accidentally injures them, as well as preventing possible cannibalism between the young.