Ultrasound scans in pregnancy
Obstetric Ultrasound is the use of ultrasound scans in pregnancy. Ultrasounds of the baby are done with real time machines which show a continuous moving image of the baby with the help of ultrasonic sound waves between 3.5-7 megahertz. The sound waves are generated by a transducer [which is placed either on the mothers abdomen-trans abdominal scan, or in the vagina-transvaginal scan], and these waves are reflected from various structures of the baby back to the transducer and this is finally shown as an image on the screen
A patient must have a full bladder for an abdominal scan although this is not required for a vaginal scan. A scan is painless and not uncomfortable.
What are the uses of a scan in pregnancy?
· Diagnosis and confirmation of early pregnancy
A scan can pick up a pregnancy as early as 41/2 to 5 weeks and also confirms that a pregnancy is inside the uterus thereby ruling out a tubal pregnancy.
9 Week Pregnancy
· Early diagnosis of multiple pregnancy
A 1st trimester scan helps in establishing an early diagnosis of twin [or more] pregnancy.
12 Week Twin Pregnancy
· Vaginal bleeding in early pregnancy
A scan for a patient with early pregnancy bleeding helps in the diagnosis of the following:
Threatened, inevitable, incomplete and missed abortions
Even a trans vaginal scan in early pregnancy does not harm the foetus.
· Determination of age and expected date of delivery [EDD]
The following measurements are taken to very accurately date the pregnancy and give an accurate EDD. In fact the first trimester scans are the most accurate to establish the EDD, as well as later to establish any growth lag if any [IUGR].
1. CRL [Crown rump length] – head
· Weight of the baby
The above measurements are also used to estimate [+/- 15%] the weight of the baby
· Abnormalities in the baby
Many structural abnormalities in the foetus can be reliably diagnosed by an ultrasound scan, and these can usually be made before 20 weeks. Common examples include hydrocephalus, anencephaly, myelomeningocoele, achondroplasia and other dwarfism, spina bifida, exomphalos, Gastroschisis, duodenal atresia and fetal hydrops. With more recent equipment, conditions such as cleft lips/ palate and congenital cardiac abnormalities are more readily diagnosed and at an earlier gestational age.
· Placenta localization
Ultrasonography has become indispensable in the localization of the site of the placenta and determining its lower edges, thus making a diagnosis or an exclusion of a low lying placenta [placenta praevia]
· Hydramnios and Oligohydramnios.
Excessive or decreased amount of liquor (amniotic fluid) can be clearly depicted by ultrasound. Both of these conditions can have adverse effects on the foetus. In both these situations, careful ultrasound examination should be made to exclude intrauterine growth retardation and congenital malformation in the fetus such as intestinal atresia, hydrops fetalis or renal dysplasia.
· Other uses
Confirmation of intrauterine death.