37 weeks pregnant: baby is the size of a leek

Your baby this week

Your baby is fully formed and practising for life outside. The lungs are ready for breathing air, and the digestive system can take milk. The brain and nervous system are still developing and will keep doing so for years. Your baby has a firm grip and may practise sucking.

Meconium, the dark, sticky first stool, has built up in the bowel. Your baby will usually pass it in the first day or two after birth. Your baby is probably head-down, with the head lower in your pelvis.

How it happens. Labour starts through a signal that is not fully understood. A mix of hormone changes in you and your baby, and stretching of the uterus, seems to trigger contractions, and the cervix softens, thins and opens.

Your body this week

Your cervix is starting to soften, and it may begin to thin out and open a little. You may have more Braxton Hicks tightenings, and you might feel pressure, an achy back or loose stools. These can go on for days or even weeks before labour starts, which is often called pre-labour or early labour.

You may feel a mix of excitement and nerves. Keep your phone charged, your bag packed and your plan ready.

Signs that labour is starting

The NHS lists these signs. Not everyone has all of them, and their order varies.

• Contractions. Regular tightening that comes at intervals and gets longer, stronger and closer together. They may feel like period pain or a tightening band around your belly or back.
• A show. The mucus plug, which has sealed the cervix, comes away as a sticky, jelly-like pink or blood-streaked discharge. This can happen days before labour, or during it.
• Backache. A persistent ache in the lower back that may come in waves.
• An urge to use the toilet. Pressure from the baby's head on the bowel.
• Your waters breaking. Fluid escapes as a trickle or a gush. Only about one in ten labours begin this way, and for most people contractions start before the waters break.

When to call, and when to go in

Each maternity unit gives its own advice. Ask yours what it prefers, especially if you live far away, had a fast labour before or have a higher-risk pregnancy.

A common rule of thumb for contractions is 5-1-1: contractions about every five minutes, each lasting about a minute, for about an hour. Once that pattern is established, call your unit. Before that, you can usually stay at home.

Call your maternity unit right away, or go in, if:

• Your contractions are regular and painful, and fit your unit's guidance
• Your waters break, whether a trickle or a gush
• You have vaginal bleeding that is more than a show, or is bright red
• Your baby is moving less, or in a different pattern
• You are less than 37 weeks, or you have a high-risk pregnancy
• You have a constant, severe pain that does not ease between contractions
• You are worried, or something does not feel right

If your waters break

Note the time, and the colour and smell of the fluid, and put on a pad. Call your unit, even if you have no contractions. Clear or slightly pink fluid is normal. If it is green or brown, or has blood in it, tell them and go in right away, since it may mean your baby has passed meconium. If you have GBS or your baby is not head-down, go in as advised. Most people go into labour within 24 hours of their waters breaking at term, and your team will explain how long they are comfortable to wait.

What to do at home in early labour

• Stay comfortable. Change positions, walk, use a ball or take a warm bath or shower.
• Eat light foods and drink fluids. Toast, fruit and soup are easy choices.
• Rest if you can. Early labour may be long, and you will need energy.
• Time your contractions. Note when each starts and its length, or use a phone app.
• Use distraction. Music, a film, a walk or a chat can pass the time.
• Keep your birth partner informed, and arrange your transport.