Pregnancy Week 39: Almost There — Overdue Options and Your Baby Ready to Be Born

8 min read

Quick answer: At 39 weeks your baby is fully developed and ready to be born, measuring around 50.7cm and weighing about 3.3 kilograms. If labour hasn't started by 40 weeks, your midwife will offer a membrane sweep, and induction is offered if labour has not started naturally by 41 weeks, because the risk of stillbirth or problems for the baby starts to increase from then. The decision about induction is always yours.

What parents need to know

You've made it to 39 weeks — your baby could arrive any day now! The vast majority of babies are born between 38 and 42 weeks, with the average being around 40 weeks for first-time mothers and slightly earlier for subsequent babies. This week, let's talk about what happens if your due date comes and goes, and what options are available.

Baby's length	About 50.7cm crown to heel
Baby's weight	Around 3.3 kilograms, like a large watermelon
Typical birth window	Most babies born between 38 and 42 weeks
Membrane sweep offered	At 40 weeks if no signs of labour
Induction offered	If labour has not started by 41 weeks

How big is your baby at 39 weeks?

Your baby now measures approximately 50.7cm from crown to heel and weighs around 3.3 kilograms, roughly the weight of a large watermelon. They're fully developed and ready to be born, with all the systems they need for life outside the womb in place.

What's happening with your baby?

Your baby's brain continues to develop, a process that will continue for years after birth. Their skin is soft and smooth, and most of the vernix caseosa (the white waxy coating) has been absorbed. Your baby is in a state of quiet readiness, conserving energy for the demanding work of birth and the newborn period. Their lungs are fully mature, their digestive system is ready, and their liver is prepared to process waste products after birth.

Understanding your options if labour doesn't start

Most women go into labour naturally before or by 42 weeks, but some pregnancies go beyond the due date. If you reach 40 weeks without signs of labour, your midwife will offer a membrane sweep. This is an internal examination during which the midwife uses a gloved finger to sweep around the cervix and detach the membranes from the cervix wall. This releases hormones (prostaglandins) that can trigger labour. It can be mildly uncomfortable but is safe and can reduce the need for medical induction.

If you do not go into labour naturally by 41 weeks, you'll be offered induction of labour. This is because the risk of stillbirth or problems for the baby, while still very small, starts to increase once you reach 41 weeks. Induction methods include prostaglandin gel or pessary applied to the cervix, a hormone drip (Syntocinon/oxytocin) to start contractions, or artificial rupture of the membranes (ARM) to break the waters. Your midwife and obstetrician will discuss the risks and benefits with you, and the decision about induction is always yours to make.

Choosing to wait for spontaneous labour

Some women choose to decline or delay induction. If this is your preference, your care team should support you with increased monitoring, including fetal heart rate monitoring and scans to check amniotic fluid levels. The RCOG recommends that all options are discussed openly and that women are supported to make an informed decision that reflects their individual circumstances and values.

When to get help

Some symptoms in pregnancy can be a sign of something serious and need checking quickly. This is who to contact, and how soon.

Call 999 if:

you're bleeding from your vagina and the bleeding is heavy (soaking a period pad soon after putting it on), or you also have severe pain in your tummy, pain in your shoulder, or feel sick, faint, dizzy or lose consciousness
you think your baby is coming now and you have a strong urge to push (ask for an ambulance)
you have severe difficulty breathing (you're gasping, choking or not able to get words out) or your chest feels tight or heavy
you have pain and swelling in one leg and you also feel short of breath or have chest pain. A blood clot in the leg can travel to your lungs, which can be life-threatening
you have possible signs of sepsis, such as breathing very fast, being confused or having slurred speech, blue, pale or blotchy skin, a rash that does not fade when you press it, or a very high or very low temperature. Being pregnant makes sepsis more likely
you do not feel you can keep yourself safe (a mental health emergency is as serious as a physical one)

Always call 999 if you think it's a life-threatening emergency, no matter what stage of pregnancy you are.

Call your midwife or maternity unit now if:

your baby is moving less than usual, you cannot feel your baby moving anymore, or there is a change to your baby's usual pattern of movements
you have light bleeding or spotting, even if you have no pain or only mild tummy pain
you have stomach pain that is severe or does not go away after you've rested for 30 to 60 minutes, or stomach pain with regular cramping or tightenings, lower back pain, or pain when you pee
you're less than 37 weeks pregnant and you have a gush or trickle of fluid from your vagina (this could be your waters breaking), regular contractions or tightenings, period-type pains, or backache that's not usual for you
your waters break, even if labour has not started
you have signs of pre-eclampsia: a severe headache that does not go away with simple painkillers, vision problems (such as blurred vision or seeing flashing lights), pain below the ribs, sudden swelling of the face, hands or feet, feeling very unwell, heartburn that does not go away with heartburn medicines, or being sick (vomiting)
your skin is very itchy (for example, it keeps you awake at night), the palms of your hands or soles of your feet are itchy, or the itching is worse at night. This can be a sign of a liver condition called intrahepatic cholestasis of pregnancy (ICP) that needs urgent treatment
your breathlessness comes on suddenly, you're out of breath when you're lying down, or you're breathless and also have chest pain or feel dizzy
you have pain or swelling in one leg, usually in the calf or thigh. This could be a blood clot (deep vein thrombosis, or DVT), which is more likely when you're pregnant
you have a high temperature (above 37.5 degrees C) with no other flu or cold symptoms, or you feel hotter than usual or shivery. A high temperature can be a sign of an infection, so it's important to get it checked
any of your contractions last longer than 2 minutes, or you're having 6 or more contractions every 10 minutes
you have brown or pink discharge

If your baby's movements change, do not wait until the next day: call immediately, even if it's the middle of the night. Do not use a home doppler to check the heartbeat yourself. Even if you hear a heartbeat, this does not mean your baby is well.

If your waters break, use a period pad (not a tampon) so your midwife can check the colour of the waters, and tell them immediately if the waters are smelly or coloured.

Call your midwife or maternity unit for guidance if you think you're in labour, or you're having regular contractions coming every 5 minutes or more often.

You can also call your midwife or maternity unit if you're unsure or worried about anything.

If you cannot reach them, or you're not sure what to do, call NHS 111.

Speak to your midwife or GP if:

you're worried about your mental health, or stress, anxiety or low mood are affecting your day-to-day life. If you need urgent help for your mental health, call 111 and select the mental health option, or ask for an urgent GP appointment

Go to sleep on your side. From 28 weeks, the safest position to go to sleep is on your side, either left or right. Research suggests that, after 28 weeks, falling asleep on your back can double the risk of stillbirth. This includes daytime naps. If you wake up on your back, just turn onto your side and go back to sleep.

Your week 39 checklist

This week:

Keep monitoring your baby's movements and call immediately if they reduce.
Ask about a membrane sweep at your appointment.
Rest, rest, rest.
Know that most babies arrive by 42 weeks at the latest, with induction available if needed.

Frequently asked questions

What is a membrane sweep and does it hurt?

It's an internal examination where the midwife sweeps a gloved finger around the cervix to detach the membranes, releasing prostaglandins that can trigger labour. It can be mildly uncomfortable but is safe, and may reduce the need for medical induction.

Can I decline induction at 41 or 42 weeks?

Yes — the decision about induction is always yours. Some women choose to decline or delay it. If so, your care team should support you with increased monitoring, including fetal heart rate monitoring and scans to check amniotic fluid levels.

What induction methods are used in the UK?

Methods include prostaglandin gel or a pessary applied to the cervix, a hormone drip (Syntocinon/oxytocin) to start contractions, or artificial rupture of the membranes (ARM) to break the waters.

Sources & further reading

General information, not individual medical advice. Speak to your GP, midwife or health visitor about your baby’s needs.