Week thirteen
At the start of the second trimester the foetus is still tiny. In week 13, it should weigh about the same as four 2 pence coins. Despite being so small, amazingly the fingers already have their very own little fingerprints.
Week fourteen
Ideally, by now you will have had your first ultrasound appointment where you can see your future baby and hear the heartbeat. The foetus can now move around a lot more energetically as its muscles develop, although this movement is not controlled by the brain yet.
Week fifteen
Lanugo starts to cover the body of the foetus. It's a fine downy hair which is shed before birth but may be seen on the bodies of premature babies. Occasionally a term baby is born with laguno still present, and baby seals are born with this hair too!
Week sixteen
The foetus is getting bigger all the time. It now is approximately the length of a small ruler. Sweat glands develop on the still transparent skin. The placenta has been growing too and is now about 1cm thick. The foetus' external genitals are forming.
Week seventeen
Bones are hardening, including the bones inside the ears. The foetus can now hear sound! Newborns have been shown to recognise the voices they hear while in the womb so don't feel silly chatting to your bump - you are getting to know each other already!
Week eighteen
Eyelashes and eyebrows start to sprout, although the eyelids are still tightly shut at this stage. Lots of funny faces are pulled around this time as your unborn baby starts to exercise the muscles needed to breathe and feed later.
Week nineteen
Although weight gain continues, growth from now on is a bit slower. The head size starts to look more in proportion with the body. The heartbeat of the foetus can now be heard with a stethoscope. Many first-time mums feel movement for the first time around.
Week twenty
Around this time you should have your second scan at hospital. Your baby's genitals are developed enough to make it possible to tell what gender he or she is if you can't wait until the birth to find out.
Week twenty one
By week 21 the sebaceous glands in the skin are making the greasy, waxy material vernix, seen here on this newborn. This is thought to protect the skin. You are well into the second half of your pregnancy now and the embryo is about 27cm long.
Week twenty two
The 22 week old embryo can now swallow some of the liquid surrounding it, and so can make its own urine. It is putting on brown fat. This fat is to keep it warm when born. Nipples appear on boy and girls at about this stage.
