Pregnancy

An Early Pregnancy scan is best performed transvaginally, although a transabdominal examination can be performed at the patient’s request.

The scan is usually performed for a specific indication such as pain or bleeding in early pregnancy, to confirm early viability in women who have previously had a miscarriage or an ectopic pregnancy and confirm multiple pregnancy in patients who have had fertility treatment.

Scanning at this gestation is to:

• Confirm the diagnosis and viability of a pregnancy
• Confirm the gestational age by measuring the crown rump length (CRL)
• Exclude an ectopic pregnancy
• Diagnose a multiple pregnancy and chorionicity (whether twins share a placenta).

This provides important information about your pregnancy. It is usually performed transabdominally but occasionally a transvaginal scan will be required to provide all the information.

Scanning at this gestation is to:

Confirm the viability of a pregnancy

At this gestation although the majority of pregnancies will be viable, a small number will result in early pregnancy loss (miscarriage)

Confirm the gestational age

Accurate dating is important to allow us to pick up whether there any changes in the baby’s growth pattern later in pregnancy. Dating of a pregnancy is also needed in women unsure of their menstrual cycle or those with irregular cycles.

Diagnose multiple pregnancy

This may be present in up to 2% of pregnancies and is even more common if fertility treatment has been undertaken. This is the best gestation to determine whether or not twins share a placenta (chorionicity) which has a major impact on the management of the pregnancy.

Screen for chromosomal anomalies (combined nuchal-biochemistry test)

Although the vast majority of babies have a balanced number of chromosomes, there is a chance of having a baby with a chromosomal anomaly such as Down syndrome. Measurement of the nuchal translucency (fluid behind the neck of the baby), together with knowledge of the mother’s age and measurement of the maternal hormones (ßhCG and PAPP-A) will allow estimation of the mother’s individual chance. Mothers with a high chance of 1:150 or greater, may then decide if they wish to have a non-invasive prenatal test (NIPT) prior to an invasive diagnostic test such as amniocentesis or chorion villus sampling

Diagnose major structural anomalies

A number of major fetal anomalies such as severe forms of spina bifida may be diagnosed at this gestation. However, we recommend a detailed fetal anatomy scan at 20-23 weeks for optimal detection of fetal anomalies.

This scan will confirm that the vast majority of pregnancies are developing normally. However, about 1% of all fetuses will have a serious congenital anomaly and ultrasound examination at this stage will detect about 70% of these. In addition, screening tests for the later development of high blood pressure (preeclampsia), poor fetal growth and premature birth can also be performed.

Detailed inspection of every organ and the fetal anatomy is performed, including the fetal brain, spine, heart, lungs, kidneys, stomach, bowel , bladder, limbs, fingers and toes.

Preeclampsia and fetal growth restriction

These conditions are caused by poor function of the placenta. Estimating the chance that severe forms of these conditions developing before 37 weeks can be made by performing non-invasive Doppler ultrasound examination of blood flow in the maternal uterine arteries.

Premature birth

About 50% of cases of spontaneous delivery before 34 weeks are associated with shortening of the cervix. Ultrasound assessment of the cervix can be performed at this assessment.

Cardiac anomalies

Although heart anomalies are rare, we advocate screening for this anomaly. If your pregnancy is at increased chance of heart anomalies or sub-optimal heart views are obtained on ultrasound, we would recommend detailed heart scanning by a fetal cardiologist.

The assessment of fetal well-being from 24 weeks involves the study of several different parameters.

Fetal growth is determined by measurement of the head, abdomen and limbs. It is then possible to estimate fetal weight which may be compared with the expected weight for that gestation.

Measurement of the amniotic fluid around the baby (liquor volume) is an indicator of pregnancy complications including diabetes and placental insufficiency.

The observation of fetal movements and fetal breathing movements are also indicators of fetal wellbeing.

Colour flow Doppler to assess fetal and maternal blood flow is a sensitive marker of the health of the baby and pregnancy. In some cases, detailed assessment of the fetal blood vessels may be recommended by your consultant.

The position of the placenta in relation to the cervix is checked to exclude a placenta praevia (low lying placenta). If the placenta was found to be low lying at your 20-week scan, your consultant will usually advise such a scan.

Most instances of poor fetal growth start in late pregnancy, but all pregnancies should be assessed at least clinically; the level of ultrasound monitoring should reflect the level of risk.  In low risk pregnancies, a fetal wellbeing scan at 36 weeks gestation is recommended by most obstetricians. In high risk women serial fetal well being scans every 3-4 weeks may be considered (serial scans).

Obstetric (pregnancy) history

• Previous small babies birth weight less than 5Ilb or 2.3 kg at 40 weeks
• Previous stillbirth
• Previous preeclampsia (high blood pressure in pregnancy)

Medical History

• If you are older than 40, have a raised body mass index (BMI) >35 or smoke
• Recurrent miscarriage
• Maternal medical conditions such as diabetes, hypertension, renal or cardiac disease
• Large Fibroids
• Antiphospholipid syndrome (APS) – a condition where the immune system produces abnormal antibodies making the blood stickier than normal

Issues arising in pregnancy

• Low PAPP-A (a pregnancy associated hormone that is produced by the placenta)
• Suboptimal blood flow in the maternal uterine arteries detected on the 20-23-week scan
• Preeclampsia
• Multiple pregnancy
• Bleeding during pregnancy
• Clinical suspicion of fetal growth restriction or increased fetal growth
• Suspected breech presentation

Detailed examination of the fetal heart is performed by a consultant fetal cardiologist. Some groups of pregnant women are recognised to be at increased risk for heart problems in their fetus.

These groups include:

• Family history of congenital heart disease
• Increased nuchal translucency above the 95th centile at the 11-13 week scan
• Maternal diabetes mellitus
• Mothers taking teratogenic drugs i.e. anticonvulsants
• Abnormal or sub-optimal cardiac views on a routine anomaly scan.

Parents may value fetal echocardiography to provide reassurance of normality even in the absence of other risk factors.

Scans are usually performed at 18-23 weeks gestation but can be undertaken from as early as 14 weeks gestation if required in some high-risk pregnancies.

If a malformation is found, parents will receive a detailed explanation and prognosis of the cardiac condition and further investigation and management will be planned as appropriate.