Health encyclopaedia - Alphabetical Topic List
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When should it be done? of Antenatal screening
Most antenatal screening is carried out in early pregnancy. Some screening tests look for abnormalities in the baby, and some look for problems with the mother’s health:
Screening for abnormalities in the baby:
Blood tests are carried out from 11-20 weeks. This measures the levels of proteins and hormones in the mother’s blood to work out the chance of the baby having a serious condition such as Down’s syndrome or spina bifida.
Combined, integrated and triple tests are types of blood test taken in early pregnancy. A combined test uses one blood test and nuchal scan (see below) to find out the baby’s chance of having Down’s syndrome. The integrated test, or alpha-fetoprotein (AFP) test, uses two blood tests taken a few weeks apart and a nuchal scan to find out the chance of the baby having Down’s syndrome. The triple test (also known as the Leed’s test or the Bart’s test) looks at the levels of blood chemicals between 16 and 18 weeks, to find out the chance of the of baby having Down’s syndrome, spina bifida or anencephaly.
The mother’s age, medical and family history is also considered alongside the results of all types of blood test.
In some areas of the UK a nuchal scan (or serum screen) is offered to women over 35 at 11-13 weeks of pregnancy. The mother has an ultrasound scan to measure the amount of fluid at the back of the baby's neck (the nuchal translucency). It’s used to work out the likelihood of the baby having Down’s syndrome - babies with Down's syndrome have a thicker layer. The mother’s age and medical history is also considered.
Fetal anomaly screening uses ultrasound scanning to find certain abnormalities in the baby. This is usually carried out at 18-20 weeks and can identify certain heart problems and conditions that may need treatment as soon as the baby is born. If this is the case, doctors can arrange for the mother to give birth in a hospital where the baby can get specialised paediatric surgery straight away.
Fetal anonmaly screening can also identify abnormalities such as cleft lip, and confirm spina bifida if blood tests have shown the baby is at high risk.
Routine screening for sickle cell and thalasaemia (inherited blood conditions) is currently being introduced across England. All pregnant women should be offered screening for these conditions by the end of 2005.
Screening for maternal disease
All mothers-to-be have regular check-ups throughout pregnancy to try to identify any ‘hidden’ health problems they may have. The maternal diseases doctors look for include anaemia, HIV, diabetes, urinary tract infections, syphilis and high blood pressure. These conditions could be harmful to the baby and cause complications such as anaemia for the mother. Bacteriuria, for example, is a urinary tract infection that can cause premature birth (being born too early) or low birth weight if it isn’t treated.
Maternal screening aims to find these problems early on – several of the tests may be carried out at one of the woman’s first antenatal appointments. This means treatment can be started early to lessen the effect of the disease on the unborn baby. Immunity to rubella is checked, so that any non-immune babies can be vaccinated after delivery, and the mother can be immunised (usually at the 6 week postnatal check). If a mother has hepatitis B, the baby can be immunised soon after birth to prevent it becoming infected as well.
