You may have noticed that you have gained weight, this is a result of a number of things.: you baby's support system (placenta, amniotic fluid etc) are rapidly developing; your uterus and breasts are enlarging and your total blood volume is increasing. During the first trimester you can expect to gain about 1-2kg, over your second trimester you can expect to gain about 6kg and over your third trimester you may gain about 5kg.
If you are underweight or over weight before pregnancy your doctor may recommend different dietary options. See our section on Diet during pregnancy for more information.
Your baby could measure up to about 5cm and weigh about 15 grams; this is expected to increase rapidly: by week 20 he or she will be about 15cms long and weigh 255 grams. In order to cope with such growth and to provide your baby with more nutrients during this time, blood vessels in the placenta are multiplying and enlarging.
Your baby's internal organs will now be developed and functioning, from now on they will grow in size and maturity. This means that from this point there is less risk of your baby developing any major congenital abnormalities.
Your baby's genitals are still developing this week, you won't be able to tell whether your baby is a boy or a girl yet but the tissue that covers this region will soon develop into either a penis or a clitoris and labia minora.