It’s the last week of the first trimester of pregnancy and the last week of the embryonic period. Up until now the baby had a very large head compared to the rest of its body, but things are starting to change.
How big is the baby on week 13?
By week 13, the embryo is about 9.5 cm in long and weighs in at about 35g, it’s around the same size as a tangerine.
What does the foetus’ body look like?
At this point, the baby’s head is about one-third of its body, and the body itself is starting to take shape. If you could see it now, you’d notice that your baby already has a human face – the eyes and ears are positioned in the right areas, even if they aren’t fully developed, and the nose and mouth are formed. The vocal cords and fingerprints are also being shaped.
At 13 weeks, the baby’s skin is transparent, very thin and delicate, it has a reddish hue due to the blood vessels underneath it.
The development of internal organs
The kidneys and the urinary tract are completely functional, and this means that the amniotic fluid that the foetus has already started to swallow can now be eliminated through urine. The embryo urinates about twice an hour.
The baby’s intestines are now in the abdomen, after having partially formed in the umbilical cord at the beginning of pregnancy. Also, this week, the baby’s skin starts being covered with delicate baby hair called Lanugo.
Lanugo is soft, light-coloured hair that all new-borns have. It’s formed during the intrauterine life and it disappears within five months from birth.
These small hairs have the role of protecting the skin and making birthing easier.