33 weeks pregnant: fetal development

Your baby now weighs about 1.9kg, almost the same as a pineapple, and measures more than 43.7cm from head (crown) to heel (Hill 2019).

Your baby's brain develops rapidly throughout the third trimester (Konkel 2018). But once he's born, and all his senses are stimulated, his brain growth will be super-charged (Konkel 2018).

Your baby's skin is becoming less wrinkled as he plumps up in preparation for birth (Hill 2019, Moore et al 2019). His arms and legs are looking quite chubby now, thanks to the amount of white fat building underneath his skin (Hill 2019, Moore et al 2019, Visembryo nd).

Your baby's skull is soft and pliable, and the plates of bone that form it aren't yet fused (Bailey 2014, Hill 2020). If you have a vaginal birth, your baby's skull plates will slide over each other as he eases through the birth canal (Bailey 2014, Hill 2020). You'll be able to see, or gently feel, the gaps (fontanelles) in your baby's skull when he's born (NHS 2018a).

The fontanelles won't all close until he's about 18 months old (Bailey 2014, Hill 2020). Throughout childhood, his skull plates remain flexibly joined to make space for his growing brain. His skull bones won't lock fully into place until adulthood (Hill 2020).

If you're having a boy, his testicles are likely to have descended into his scrotum by now (Favorito and Sampaio 2014, Moore et al 2019). Sometimes, though, one or both testicles don't fully descend until after birth. This is especially common in babies who are born prematurely, or with a low birth weight (NHS 2018b, NICE 2020). If your baby is born with undescended testicles, they should move down into his scrotum by about three months (NICE 2020).

Check out our pregnancy guide to see what changes could be happening to you at 33 weeks pregnant.