24 Weeks!

By 24 weeks your twins are proportioned like newborns but thinner - their "baby" fat hasn't yet developed. Although they're getting heavier every day, their skin still appears wrinkled because they need to gain more weight. Their lips are distinct and their eyes are formed, though the iris (the coloured part of the eye) still lacks pigment. The pancreas and the thyroid, adrenal and pituitary glands, essential in the production of hormones, are developing steadily. Tiny eyebrows and eyelids are now visible. 

Even this early, the first signs of teeth appear in the form of tooth buds beneath the gum line. Before you know it, your twins will be born, and soon after, their first teeth will come through. 

Your twins' lungs continue to develop and mature to prepare for breathing. They're swallowing but they normally don't pass their first stool (called meconium) until after birth. Your babies are making breathing movements. They have no air in their lungs yet but it's essential practice for when they are born. 

*****More than half of twins are born before term (before 37 weeks). If your babies were to be born before 24 weeks, they would only have a small chance of survival (less than 10 per cent) even with the right care. Every day in the uterus makes a difference at this stage. Their chance of survival rises rapidly after 26 weeks, and from 32 weeks they should survive if they are growing normally. ******