18 weeks pregnant

Your baby at 18 weeks

Eighteen weeks sits in the middle of ACOG's 17-to-20 week band, when several systems reach a working state. The part of the brain that controls movement is fully formed, and the gut has started to work. On an ultrasound screen a sonographer can now make out the ears, nose and lips. Soft, fine lanugo hair begins to grow over the body. In girls, ACOG adds, the womb and vagina are beginning to develop.

Your baby today is a bell pepper in the fruit comparison, and 14.2 cm from crown to rump. The length is measured that way because the legs are still folded and difficult to stretch out on screen. A weight this early is an estimate. The WHO fetal growth charts (Kiserud and colleagues, 2017) are built from ultrasound measurements taken on healthy babies, and they give 222 g as the middle estimated weight at exactly 18 weeks, with the 10th percentile at 192 g and the 90th at 255 g. Head circumference follows the same chart: 148 mm in the middle.

Two healthy babies of the same age can sit at quite different points in that range. A scan estimates rather than weighs, and a care team follows the trend from one visit to the next rather than reading a single measurement in isolation.

What makes 18 weeks special is timing. It is the first week of the standard mid-pregnancy scan window, so for some people the next few days bring the first detailed look at their baby. The weeks before the scan are a good time to find out how your hospital runs it and to decide what you want from the appointment.

Your body at 18 weeks

Many people have a visible bump by this point, though how soon it shows differs a lot from one pregnancy to the next. The NHS links back pain in pregnancy to ligaments softening ahead of labor, and as the bump grows, a comfortable sleeping position can get harder to find.

You may start noticing your baby. The NHS describes the earliest movements as a gentle swirling or fluttering, becoming kicks and jerks later on, and says most people feel them between 16 and 24 weeks. In a first pregnancy, the NHS says, you might not feel them until after 20 weeks.

Appointments in England follow a rhythm. The NHS lists a visit at 16 weeks, then the screening scan between 18 and 21 weeks, and for a first pregnancy a further visit at 25 weeks. Your clinic or hospital may set different dates, so use their schedule as your guide. A US practice will follow its own visit calendar.

Common symptoms around 18 weeks

• First flutters. A light flicker low in your belly may be your baby. There is no fixed day when it begins, and the first movements are faint enough that you may not be sure at first.
• Lower back ache. Softer ligaments strain the back and pelvis, says the NHS. Wear flat shoes, bend your knees to pick things up, and sit with your back supported.
• Heartburn. The NHS says it is more common from 12 weeks onward. Try smaller meals, upright posture after eating and a gap of three hours before bed.
• Poorer sleep. As the bump grows, lying comfortably gets harder. The NHS says side sleeping is the safest position, with a pillow between your knees or under the bump for support.

Tips for this week

• Ask how your scan works. Find out whether you need a full bladder, whether you can bring someone, and whether you will be told the sex if you want to know. The NHS says most hospitals do not let children into the scan room.
• Wear loose clothes on scan day. The sonographer needs easy access to your tummy, and the NHS suggests taking out a belly piercing if you have one.
• Think about what you want to know. The NHS says the scan is your choice. You can decline it, or have it and ask not to be told the sex.
• Do not lie flat for long. The NHS advises avoiding anything that has you flat on your back for more than a few minutes in later pregnancy, because it can make you feel dizzy.
• Stay active. Walking and swimming are easy ways to reach the NHS's suggested 150 minutes of moderate activity a week.

When to call your doctor or midwife

Match the call to the symptom. Heavy bleeding, severe pain, fainting or pain at the tip of a shoulder: your local emergency number, now. Light spotting or mild cramps: your midwife or doctor the same day, or an early pregnancy unit while you are under 20 weeks, with your local non-emergency health line as the backup.

• Call the same day if you have light vaginal bleeding, even with no pain or only a mild tummy ache. The NHS says to call your maternity unit or early pregnancy unit for urgent help.
• Call your emergency number if the bleeding is heavy, or if it comes with severe tummy pain, pain in your shoulder, or feeling sick, faint or dizzy.
• Call now if you have been feeling your baby move and the movements slow, stop or change from their usual pattern. Phone your midwife or maternity unit straight away; the NHS says not to wait until the next day. Neither the NHS nor the RCOG asks you to count kicks to a set number; if your own provider does, follow their advice.
• Call now if morning sickness has not settled and you cannot keep down food or drink for a full day, or you are barely peeing and feel dizzy when you stand.
• Call now if it burns or hurts when you pee, or if back pain comes with a fever, bleeding or pain under your ribs.
• Tell your midwife if you have not felt any movement by 24 weeks.