Ultrasound scanning has been in use in pregnancy care since 1978 and most countries have incorporated routine ultrasound scanning in early pregnancy between 11 and 14 weeks, in their antenatal care policy.
The unbelievable but commendable achievement in Sri Lanka is that 80% of women “book” (register) with the midwife before they complete the 8th week of pregnancy, according to the 2009 statistics of the Family Health Bureau. With Sri Lanka’s maternity care setup being world recognized, the country should now be in a unique position to offer these expectant mothers early pregnancy scanning.
It is of paramount importance to “date the pregnancy” not only to monitor the growth of the foetus but also to have an accurate idea about the date of delivery. Usually, the assumption is that the “dropping of an egg” occurs on the 14th day but there is no guarantee that it is not sooner or later. A simple but early scan will point the doctor towards the right date of delivery.
One of the main benefits of scanning in early pregnancy is the ability to date the pregnancy accurately which in turn will help find the delivery date and avoid complications.
Accurate pregnancy dating
The calculation of gestational age and the expected date of delivery is not just a social issue but has considerable medical implications. For many centuries it has been accepted that the normal pregnancy period for humans is 10 lunar or nine calendar months.
Dating a pregnancy by menstrual (period dates) history may not be accurate because up to 40% of women are uncertain of their menstrual dates while the release of an egg (ovulation) may not exactly correspond with the mid-menstrual cycle. Dating the pregnancy by ultrasound examination in the first trimester (between 11 and 14 weeks) has proven more reliable than methods based on the date of the last menstrual period. Ultrasound dating can reduce the percentage of pregnancies that will go beyond due date (post-term pregnancies) up to 60%.
Some of the other benefits are:
Screening for Down’s
syndrome
The traditional method of screening for Down’s syndrome has been based on maternal age alone. Taking a sample of fluid around the baby (Amniocentesis) or taking a sample of placenta (chorionic villous sampling) was offered to women aged 35 years or more. As a majority of affected foetuses are from the younger age group, this practice is not able to detect more than half of the babies with Down’s syndrome. Further, these tests carry a 1-2% risk of miscarriage.
A more effective method of screening is based on the combination of the mother’s age, sample of the mother’s blood for placental products (free ß-hCG and PAPP-A) and an ultrasound scan at 11-14 weeks to measure the collection of fluid behind the baby’s neck (nuchal translucency). This combination will detect 90% of babies with Down’s syndrome.
Early diagnosis of many major abnormalities of the baby
Many major structural problems (brain, abdominal wall, limb etc.) can be diagnosed with a scan done between 11- 14 weeks.
The detection of twin pregnancies with reliable diagnosis of whether both twins are getting blood from the single placenta (afterbirth) or two different placentas.
Twins account for about 1% of all pregnancies with two-thirds being dizygotic (non-identical) and one-third monozygotic (identical). In non-identical twins each baby has its own placenta and amniotic sac (dichorionic, diamniotic). In identical twin pregnancies there may be a sharing of the same placenta (monochorionic), amniotic sac (monoamniotic) or even foetal organs (conjoined or Siamese).
Pregnancy complications are five times higher if the twins share the same placenta.
An ultrasound scan between 11 and 14 weeks can reliably (99-100%) diagnose whether twins are dichorionic or monochorionic.
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