Congratulations on being 16 weeks pregnant with Twins! It’s an exciting yet overwhelming time, with so much to learn about the Twins fetal development and we are here to help you every step of the way.

By 16 weeks, your twins will each measure about 12cm (4.7in), from head to bottom (crown to rump). They now weigh about 100g (0.2lb) each.

Your twins’ unique fingerprints have almost finished forming, and their fingernails are growing. They may even have started sucking the thumb of their preferred hand. If you spot one of your babies sucking their left thumb at an ultrasound scan, they may well grow up to be left-handed!

By now, your twins’ genitals may be developed enough for a sonographer to tell whether you’re expecting two boys, two girls or one of each sex. If you’re having a girl, she will already have several million eggs in her ovaries.

Your twins’ bodies are now growing faster than their heads. Their skin is covered with thick, downy hair (lanugo). This will usually disappear before the birth, although some babies are born with it.

Your babies’ legs are getting longer, and all their joints and limbs can move. Their skeletons are still soft at this stage, mostly made from rubbery cartilage that is slowly hardening.

Your twins’ chests move up and down to mimic breathing. But rather than air, they’re taking in amniotic fluid.

For these and more fascinating facts, be sure to see the Baby Centre.

Twin Classes

Now is a great time to start educating yourself on the wonderful world of Twins. Join our local group classes worldwide or stay in the comfort of your home and login to our live online classes. Let us support you on your journey to multiples and beyond!