Foetal Abnormalities

In the uterus, there are 3 variables that we monitor concerning the baby’s position.

Lie:

– This is the relationship between the long axis of the fetus and that of the mother

– It can be longitudinal, transverse or oblique

Presentation:

– This describes the part of the fetus that first enters the maternal pelvis

– Can be cephalic vertex (headfirst), breech, shoulder, face and brow

Position:

– This describes the position of the foetal head as it exits the birth canal

– Can be occipito-anterior (ideal), occipito-posterior or occipito-transverse

Abnormal lies, presentations and positions all increase the chances of complications during delivery:

Breech Presentation 

This is a  situation when the caudal end of the fetus is the first part to enter the maternal pelvis.

– This is problematic as it can lead to complications for both the fetus and the mother during delivery.

It is split into 3 types:

– Frank –> this is the most common where buttocks occupy the lower segment

– Complete –> this is where the complete caudal end of the fetus is in the lower segment

– Footling –> this is the most dangerous form where the foot is in the pelvis

Risk factors

– Mother –> Malformations of the uterus, large fibroids, previous uterine surgery

– Pregnancy –> Placenta Praevia, poly/oligohydramnios, prematurity

Complications:

– Higher rate of cord prolapse, PPROM and birth asphyxia

– Entrapment of the foetal head, intracranial haemorrhage

Diagnosis:

– Ultrasound is the investigation of choice

Management:

If <36 weeks:

– No action is required yet as many foetuses will turn spontaneously to cephalic presentation

If >36 weeks:

– 1st line is external cephalic version (ECV) to turn baby into cephalic presentation

– It is offered at 36 weeks for 1st time mothers and 37 weeks for multiparous women

– However, this cannot be offered if there are multiple pregnancies or ruptured membranes

– In addition, do not perform is worry about the fetus with abnormal CTG

If unsuccessful:

– Offer elective Caesarean section or vaginal breech delivery

– In reality most mothers nowadays will opt for an elective caesarean section rather than attempt a vaginal breech delivery

Foetal Size/position abnormalities

It is important to monitor the size of the baby, as both small and large babies are associated with complications

– Babies are measured during the antenatal scans using ultrasound, which measures certain variables

– These include abdominal and head circumference and femur length to calculate estimated foetal weight (EFW)

– In addition, you can use Doppler ultrasound to measure the flow through the vessels like the umbilical artery

– The EFW is plotted on a growth chart to see the trend and assess if the baby is following a steady trajectory.

Small for gestational age (SGA)

This term is used to describe a fetus/infant which is exceptionally small for its age compared to the average

– Infant SGA –> this is an infant born with a weight < 10th centile

– Foetal SGA –> fetus with estimated foetal weight (EFW) or abdominal circumference (AC) < 10th centile

It is helpful to divide SGA babies into 2 subtypes, as the management is very different:

Constitutionally small:

These infants are small without a pathological reason

– This is usually due to inherited genes and characteristics from the parents

– Therefore, their size is what is expected of them 

Growth restriction:

This is a term which is used to describe pathological restriction of the genetic growth potential, and so it is called pathological SGA

– Foetal or maternal features stop the fetus achieving its genetic growth potential

– It is this subtype which has higher risk of postnatal complications

Causes:

– The causes can be divided into maternal and foetal factors:

Maternal:

– Maternal anaemia, under-nutrition (gives poor diffusion of substances across placenta)

– Pre-eclampsia, hypertension, diabetes, maternal substance abuse (reduced blood flow to the placenta)

Fetus:

– Chromosomal abnormalities, infection, errors of metabolism, genetic disorders

Types:

i) Asymmetrical:

– This is a type of restriction where the head grows normally out of proportion of the body

– It is usually seen when baby grows normally in first 2 trimesters and then has problems in the third

– This leads to a compensatory mechanism to preserve flow and nutrients to the brain at the expense of other less important tissues

– This is usually due to maternal (placental) factors that’s affects the baby at later gestational ages

ii) Symmetrical:

– This is called global growth restriction and it where the baby is small proportionately

– This will occur if the baby is affected at a very early stage and so has always developed slowly

– These babies are more likely to have permanent neurological damage

– This is usually due to foetal factors (infections, genetic disorders) but also chronic maternal issues (long term anaemia, or substance abuse)

Management:

All women are assessed at booking and again at 20 weeks for risk factors for SGA

– If high risk factors for SGA –>  Serially assess foetal size and umbilical artery Doppler from weeks 26-28

– If SGA detected –> Serially assess of foetal size and umbilical artery Doppler every 2 weeks

– If the baby continues to be small, it is likely that they will be delivered early by C-section

Large for Gestational Age (LGA)

This term is used to describe a fetus which is exceptionally large for its age compared to the average

– Infant LGA –> this is an infant born with a weight > 90th centile

– Foetal LGA –> fetus with estimated foetal weight (EFW) or abdominal circumference (AC) > 90th centile

Causes:

– Maternal diabetes (Type 1 or gestational)

– Genetics –> Beckwith-Wiedemann syndrome

Complications:

The main problem is that it leads to increased problems during delivery

– Birth trauma (especially shoulder dystocia)

– Polyhydramnios

Management:

Monitor growth, if very large maybe induced early or opt for elective caesarean section