13 weeks pregnant: fetal development

Medically reviewed by Joseph Aquilina, Consultant obstetrician and gynaecologist

Your baby is now the length of a pea pod, about 7.4cm from head to bottom (crown to rump). He weighs nearly 23g (Hill 2019).

Advertisement | page continues below

Tiny fingerprints unique to your baby are forming on his fingers. Their final pattern will be set by the time you reach mid-pregnancy (Moore et al 2019a). Now that he’s discovered how to suck, he’ll be busy practising his new skills. He may even be sucking his thumb (NHS nd, Visembryo 2017).

Loops of intestines, which have been developing in the umbilical cord where it joins your baby's tummy, have moved into his abdomen (Moore et al 2019b).

Your baby is beginning to swallow amniotic fluid (Moore et al 2019b). The fluid is mostly water, but it also includes protein, carbohydrates, fats and enzymes (Moore et al 2019c). Any remaining fluid is turned into urine by his kidneys, which he will wee back into the amniotic fluid (Moore et al 2019b).

If your baby's a boy, his testicles have now formed, and his penis is growing (NHS 2018). If you're having a girl, her ovaries are developing (NHS 2018) and already contain about two million eggs (Moore et al 2019d).

Discover how pregnancy can affect your body and your life at 13 weeks pregnant.

VIDEO

Note: Every baby develops differently. This page is designed to give you a general idea of how a fetus grows in the uterus.

Advertisement | page continues below

<< 12 weeks

14 weeks >>

Don't forget to download our free app for a day-by-day guide to your pregnancy. My Pregnancy & Baby Today gives you all the expert advice you need, right at your fingertips.

Was this article helpful?

Yes

Track your pregnancy on our free #1 pregnancy & baby app

Sources

BabyCenter's editorial team is committed to providing the most helpful and trustworthy pregnancy and parenting information in the world. When creating and updating content, we rely on credible sources: respected health organisations, professional groups of doctors and other experts, and published studies in peer-reviewed journals. We believe you should always know the source of the information you're seeing. Learn more about our editorial and medical review policies.

Hill MA. 2019. Fetal development. University of New South Wales, Embryology. embryology.med.unsw.edu.auOpens a new window [Accessed March 2020]

Moore KL, Persaud TVN, Torchia MG. 2019a. Integumentary system. Chapter 19 in The developing human: clinically oriented embryology. 11th ed. Elsevier

Moore KL, Persaud TVN, Torchia MG. 2019b. Fetal period: ninth week to birth. Chapter 6 in The developing human: clinically oriented embryology. 11th ed. Elsevier

Moore KL, Persaud TVN, Torchia MG. 2019c. Placenta and fetal membranes. Chapter 7 in The developing human: clinically oriented embryology. 11th ed. Elsevier

Moore KL, Persaud TVN, Torchia MG. 2019d. First week of human development. Chapter 2 in The developing human: clinically oriented embryology. 11th ed. Elsevier

NHS. 2018. You and your baby at 13 weeks pregnant. NHS, Health A-Z. www.nhs.ukOpens a new window [Accessed March 2020]

NHS. nd. Week-by-week guide to pregnancy: second trimester. Week 13. NHS, Start 4 Life. www.nhs.ukOpens a new window [Accessed March 2020]

Visembryo. 2017. Why are you left or right handed? The Visible Embryo. www.visembryo.comOpens a new window [Accessed March 2020]