Your babies brains and nervous systems are developing rapidly. The sensitivity for negative side effects of alcohol, tobacco and certain types of medication is great when you’re 10 weeks pregnant with twins. Baby size & development Your babies measure about 3,5 cm (1.38 inch) from head to rump. Your babies heads are almost as large as the rest of their bodies. Their brains are developing rapidly. Their nervous systems are in full development. The nerve cells in their brains are forming thousands of…