39 weeks pregnant: fetal development

Medically reviewed by Joseph Aquilina, Consultant obstetrician and gynaecologist

It's all about watching and waiting now, as your baby may make his arrival any day! He could be 50.7cm in length, and weigh more than 3.3kg (7.2 pounds) (Hill 2019), about the same as a mini-watermelon. But these are only average figures.

All of your baby's organs are well developed (Moore et al 2019a). His skin is becoming thicker and paler as new skin replaces the outer skin cells that are sloughing off (Visembryo nd). His lungs are producing more surfactant, the substance that keeps his tiny air sacs open, and he's ready to take his first breath outside your uterus (womb) (Moore et al 2019b, Visembryo nd).

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Immediately after birth, your baby may cry or splutter to clear his airways. And it may take him a few minutes to establish a breathing pattern. Newborns tend to breathe irregularly, switching between fast and slow breaths (WebMD 2019), sometimes pausing for about five seconds at a time (MacLean et al 2015).

After a skin-to-skin cuddle, and time for a first breastfeed, your midwife will weigh your baby and check his head circumference (NCCWCH 2014).

Then your midwife or a paediatrician will check your baby's general health using the Apgar scale (NCCWCH 2014, Tidy 2016). The Apgar is designed to assess a newborn's heart rate, breathing, muscle tone, reflexes and skin tone (Tidy 2016).

Check out our pregnancy guide to see what changes could be happening to you at 39 weeks pregnant.

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

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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.ed.auOpens a new window [Accessed April 2020]

MacLean JE, Fitzgerald DA, Waters KA. 2015. Developmental changes in sleep and breathing across infancy and childhood. Paediatr Respir Rev 16(4):276-84

Moore KL, Persaud TVN, Torchia MG. 2019a. Moore KL, Persaud TVN and 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. 2019b. Respiratory system. Chapter 10 in The developing human: clinically oriented embryology. 11th ed. Elsevier

NCCWCH. 2014. Intrapartum care for healthy women and babies. Updated February 2017. National Collaborating Centre for Women's and Children's Health, NICE clinical guideline, 190. www.nice.org.ukOpens a new window [Accessed April 2020]

Tidy C. 2016. Neonatal examination. Patient, Professional Reference. patient.infoOpens a new window [Accessed April 2020]

Visembryo. nd. 38 wks post ovulation: abdomen is large and round as fetal liver is producing blood cells. www.visembryo.comOpens a new window [Accessed April 2020]

WebMD. 2019. Your newborn baby's breathing noises. WebMD, Grow. www.webmd.com/parentingOpens a new window [Accessed April 2020]

Megan Rive

Megan Rive is a communication, content strategy and project delivery specialist. She was Babycenter editor for six years.

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