Your baby

Having gained another two centimetres this week, your little one is now around 12cm from crown to rump and 14cm from head to toe, having doubled in weight since last week to all of three ounces.

Until now your baby’s head has grown quicker than anything else, but now your baby’s body is catching up, so that he begins to look more in proportion. However your baby has not yet developed a layer of fat, and his skin is so thin you can see the blood vessels below.

The bones are starting to harden now. Your baby's head is held high and his limb movements are co-ordinated, so that he can now make a fist, grip firmly and suck his thumb, which you might be able to see on an ultrasound. Your baby even starts to make rooting movements, as if searching for a nipple.

Your baby's face is now becoming much more detailed. The eyes have come closer together so that they face forward, and eyebrows and eyelashes are starting to grow. Although your baby’s eyelids will remain closed until about week 25, your baby can detect changes in light through his thin eyelids.

Your progress

If your pregnancy is straightforward, these are probably the weeks when you will feel at your best. Your heart rate has now increased by about 20%, so you are benefiting from an increased flow of blood throughout your body. As a result your skin is firmer and smoother and you may be glowing with health. Even your nails and hair will grow faster.

However, many women experience less welcome symptoms as pregnancy progresses. You may become constipated as the hormone progesterone slows down your digestion and your growing uterus pushes on your bladder and bowel. So try to drink two litres water each day.

Nasal congestion can be caused by high hormone levels, which swell the mucous membranes. Your increased blood supply can also put pressure on the capillaries, causing nosebleeds. Increasing in your consumption of vitamin C-rich foods may help, but do not use nose drops, unless recommended by your doctor.

What to think about

Throughout pregnancy, you will be given routine checks by doctors and midwives at an ante-natal clinic or health centre. These are carried out to ensure that both you and your baby are in good health. You may be offered blood-screening tests for spina bifida or Down’s syndrome this week.

Remember that not all hospitals routinely provide all the screening tests available. If they are not available locally, you can be referred to another centre where they are performed. It’s worth asking your midwife or GP which tests are available at your local hospital. However, here’s a quick guide to the most common tests at 16 weeks.

The AFP Blood Test - Maternal Serum Alpha Feto Protein

This is a simple blood test carried out between the 16th and 18th weeks of pregnancy. It is a screening procedure - not an accurate diagnostic test - to measure your level of alpha feto protein. A high level indicates the possible presence of a neural tube defect, eg spina bifida . A low level indicates the possible presence of Down's Syndrome. But even if a high or low AFP level is detected, it does not necessarily mean that there's something wrong with your baby. Other tests, such as a detailed ultrasound scan and/or amniocentesis, are required to confirm the presence of a neural tube defect. The AFP blood test carries no risk to you or your baby and the results are normally available within a few days to a week.

Ultrasound

An ultrasound scan is often used between the 12th and 16th week of pregnancy to confirm the age of the baby. However, ultrasound scans to detect serious abnormalities need to be performed at approximately 18-20 weeks. Most centres offer a scan at this time to check that the baby is developing as expected. This ultrasound should pick up most cases of neural tube defects (such as spina bifida) and hydrocephalus. An ultrasound scan is a non-invasive technique and there is no known risk to the health of either mother or baby.

Amniocentesis

Amniocentesis is usually carried out between the 16th and 20th weeks of pregnancy. The main use of this test is to detect chromosonal disorders (e.g. Down's Syndrome). A fine needle is inserted into the mother's abdomen and a small amount of the amniotic fluid surrounding the baby is withdrawn. The fluid is then sent to the laboratory for testing. The results for detection of neural tube defects and other structural abnormalities are normally available within a week. Results will take about three or four weeks for other conditions such as Down's Syndrome; Turner's Syndrome, inherited metabolic disorders and certain sex-linked conditions. However, unfortunately amniocenetesis carries a slight risk of miscarriage (less than 1%) so the test is not performed routinely.

Chorionic Villus Sampling - CVS

Chorionic Villus Sampling is used to diagnose conditions which otherwise couldn’t be detected until about 16 weeks of pregnancy. This test is usually only carried out if a woman is considered to have a greater risk of carrying a baby with an abnormality. It may be carried out at 10-14 weeks, or possibly at 18-20 weeks if your second ultrasound indicates there might be a problem.

In this test an ultrasound is used again to show the position of the placenta, a tiny fragment of which is removed for tests. Results are available fairly rapidly - from 2-12 days. It’s not certain what the miscarriage rate is for the CVS test in the first trimester, although it is felt to be slightly higher than for amniocentesis. However, if CVS is performed around the 18 week stage, then the risk of miscarriage is probably about the same as for amniocentesis.