FETAL GENETIC ABNORMALITIES
A gene is a defined piece of genetic information that contains the instructions required for a particular function of a cell and cell processes to manufacture a particular protein. One of the biggest concerns prospective parents have is whether their baby will be born healthy.
ARE ALL BIRTH DEFECTS HEREDITARY?
Disorders may results from abnormalities in one or more genes or in the chromosomes. Some disorders are hereditary while others are said to occur sporadically. Disorders that are not hereditary may be a result genetic material damage caused by drugs, chemicals or other damaging substances such as X-rays.Birth defects such as cleft lip or palate may result from abnormalities in one or more genes and exposure to certain factors and substances in the environment (multifactorial inheritance).
The abnormal gene causes the foetus to be more prone to a birth defect. However, the defect doesn’t develop unless specific substances such as drugs or alcohol are involved. Some common birth defects such as heart malformations are inherited this way.Neural tube defects are birth defects of the brain or spinal cord. A few neural tube defects result from hereditary abnormalities in a single gene, chromosomal abnormalities or from exposure to drugs.Some examples are:
- Spina bifida (The spine does not completely close, sometimes exposing the spinal cord)
- Anencephaly (A large part of the brain and skull is missing).
Statistics in the United States show that neural tube defects occur in about 1 in 1,000 births. Most of these defects, inheritance is multifactorial which means the influences consist of abnormal genes and other factors. Some other factors may include:
- Family history: The risk is increased when a family member (including siblings) is diagnosed with such a defect. Couples who have had a baby with spina bifida or anencephaly have 2 to 3% risk of conceiving another baby with one of these defects. The risk increases to 5 to 10% for couples who have had two children with one of these defects. However, about 95% of neural tube defects occur without family history.
- Folate deficiency: Low folate (a vitamin) may also increase the risk. Folate supplements should be taken to help prevent neural tube defects. Daily folate supplements are routinely recommended for all women of childbearing age, particularly for pregnant women. Prenatal vitamins normally consist of folate supplements.
- Geographic location: The risk also varies based on geographical locations. For instance, the risk is higher in the United Kingdom than in the United States.
Prenatal diagnosis by amniocentesis and ultrasonography is highly recommended for couples who have at least a 1% risk of having a baby with a neural tube defect.
PRE-CONCEPTION SCREENING AND COUNSELLING
Intended to assess the health of a woman planning for pregnancy while at the same time to identify existing risks:
- Which may have gone undetected before
- For women who may become pregnant
- Which may affect a foetus if the woman does become pregnant
Awareness of pre-existing conditions of potential problems allows the appropriate investigations and interventions to be performed. This will optimise the pregnancy outcome for both mother and baby. For women who are thinking of becoming pregnant should go for pre-conception screening and counselling.
CERVICAL LENGTH ASSESSMENT
Sonographic measurement of cervical length is useful in 3 ways:
- The prediction of pregnancies at high-risk of early preterm delivery
- Distinction between true and false labour in women presenting in threatened preterm labour
- Prediction of likelihood of caesarean section after induction of labour
Antenatal care before birth including non-invasive (cell-free fetal DNA) and invasive (amniocentesis) diagnosis with first trimester screening, detailed ultrasound fetal anomaly scan, follow up of high risk pregnancies and multiple pregnancies (twins and above). This care should start as soon as the pregnancy is confirmed. Healthy women with uncomplicated pregnancy should have antenatal check-ups once a month for 32 weeks of pregnancy and then twice a month until 36 weeks of pregnancy and weekly check-ups in the last 4 weeks of pregnancy.
First visit:A detailed assessment of the woman’s health, ultrasound to check on the pregnancy and blood tests to check the woman’s blood group type and any condition that could potentially affect the baby such as:
- Hepatitis B
- Human Immunodeficiency Virus (HIV)
The following visits will include assessment of the pregnant women’s well-being, weight, blood pressure, urine tests (for sugar and protein) and growth of the foetus. Additional tests and ultrasound scan may be recommended depending on the clinical condition of the woman and her foetus.
This test analyses a sample of the fluid surrounding the foetus in the womb (amniotic fluid). It is conducted from 15 weeks of pregnancy onwards.
Ultrasound is used to guide the way. A fine needle is then inserted through the mother’s abdomen and into the fluid surrounding the foetus. About 20ml of amniotic fluid is obtained and sent for analysis.
CHRONIC VILLUS SAMPLING (CVS)
This test analyses a sample of the placenta and is normally performed from 11 weeks onwards.
Ultrasound is used to guide the way. A needle is then inserted through the mother’s abdomen into the developing placenta. Suction is applied and a small sample of tissue is sent to the laboratory.
This procedure lasts for 5 to 10 minutes. It may be a little more uncomfortable than amniocentesis for the mother while the foetus is unaware of the procedure.
Modern techniques allow a preliminary result to be available within 48 hours. Final results will be ready in two weeks.