Having a large for gestational age (LGA) baby

What is a large for gestational age baby (LGA)?

A Large for gestational age baby (LGA) is a baby that is measuring on or above the 90th centile on your GROW chart within your antenatal records. This means the baby exceeds the expected weight for its gestational age (weeks pregnant). Approximately 5-8 out of 100 (5-8%) of all babies born are identified as LGA.

Whether the baby is large for you, will depend upon your own individual characteristics. This is at present defined using your customised GROW chart for your baby which would have been created at your 12 week scan appointment. Babies may be called large for gestational age if they weigh more than 9 in 10 babies (90th percentile).

Why does it matter if my baby is large for gestational age?

Most babies, even large babies, will have no problems. Evidence shows that 90% of people who go into labour carrying a baby who is suspected of being large for gestational age are able to have a vaginal birth, however, the risks to you and baby begin to rise with increasing birthweight above 4.5kg or greater than 97th centile for growth on the growth chart by USS assessment.

What causes a baby to be LGA?

It is very difficult to say what causes a baby to become LGA however we do know that the following women are at risk of having a baby which is LGA:

  • A woman who has had a previous large baby
  • A body mass index over 35 in pregnancy
  • Women who are known to have pre-existing diabetes or develop diabetes in pregnancy also known as gestational diabetes.

What are the risks of having a large for gestational age baby?

Most babies that are LGA pose minimal risk and are delivered normally with no complications, however it is important that women are aware of any increase of risk involved, these include:

  • An increased chance of having a caesarean section or instrumental birth may be needed
  • Very rarely the baby’s shoulders may struggle to come through the pelvis (this is called shoulder dystocia) (0.5% or 1 in 200 non-diabetic people). Doctors and midwives are especially trained to deal with this situation. However, very rarely, shoulder dystocia may lead to birth injuries including fractured clavicle (collar bone) or Erb’s palsy (upper arm nerve damage).
  • An increased risk of you having a large blood loss after the birth (postpartum haemorrhage)
  • An increased risk of you having a bad tear of the perineum, requiring stitches in theatre under anaesthetic (up to threefold if you are having your first baby)

How do we diagnose LGA?

During your pregnancy you will have a customised GROW chart prepared for you, based on information such as your height and weight, and the number of babies you have had and their weights, and your ethnic group.

The lines on the growth chart are called centiles (or percentiles) and show the expected pattern of growth for your baby in the ongoing pregnancy. At every antenatal appointment after 26 weeks, the distance between the top of your womb and the bone at the front of your pelvis is measured (the symphysis fundal height). This measurement is then plotted on your customised growth chart. If the measurement plots on or above 90th centile your community midwife will refer you for an ultrasound scan to measure the growth of your baby at approximately 35-36 weeks.

If you are already receiving regular growth scans due to your identified risk factors (identified at your first obstetric consultant appointment) then your abdomen won’t be measured and you will receive growth scans as planned.

During the scan, the sonographer will measure your babies femur length (hip bone), abdominal circumference, and the fluid level around baby. These measurements are then used to create an estimated fetal weight for your baby. This is plotted on your grow chart, and if the baby is plotting on or over the 90th centile then a diagnosis of LGA will be made. Please note that sometimes the growth can reduce later in pregnancy.

This will be reviewed at your next consultant appointment. If you are not currently seeing an obstetric consultant, then an appointment will be arranged for you.

Please note that accuracy of predicting your baby’s weight is reduced as the pregnancy progresses, and in 10-15% can be inaccurate.

What will happen if my baby is LGA on ultrasound?

If your baby’s weight is detected to be over the 90th centile, it is recommended that you have screening for gestational diabetes if this has not already been completed in the last six weeks. You will be offered this following the scan.

You will also be asked to attend an antenatal clinic appointment after your growth scan (within seven days) with a consultant obstetrician or a member of the obstetric team. This will be to discuss an individualised plan on how to proceed with the rest of the pregnancy. At this point you will be given the opportunity to ask questions and be involved in the decision making regarding the rest of your pregnancy including delivery.

Is there anything I can do to reduce the risk of having a LGA baby?

It is usually difficult to predict who will have a large baby and there is not very much that can be done to reduce the risk. However, eating a healthy diet and doing regular exercise can help reduce the risk if you are overweight. You can contact your Midwife to give you more advice about this and refer you to a dietician if required.

What are the risks involved in having a LGA baby?

  • Shoulder dystocia – this is where the baby’s shoulder gets stuck against your pubic bone. This occurs in approximately 0.5% of LGA deliveries however this can increase to up to 50% if the baby is deemed over 4.5kg (macrosomic)
  • perineal tearing – this will be repaired immediately by your midwife or obstetrician
  • Instrumental delivery or Emergency caesarean section

Useful sources of information

1. Shoulder Dystocia RCOG Green Top Guideline No. 42

At the Queen Elizabeth Hospital Maternity Unit, we advocate a shared decision making approach to all decisions made by our patients. This leaflet aims to give you additional information and to act as a point of reference following a discussion with your obstetrician or midwife. If you are asked to make a decision about your own care please make sure you have asked all the questions you need to ask and are given the appropriate time to do so. Some questions you might want to ask could be;

  • What are my options?
  • What are the pros and cons of each option?
  • Who will support me making the decision that is the right one for me

Contact number

If you need any you have any additional queries please contact:

Your Community Midwife on 0191 445 5306 (08:30-16:30)

The Pregnancy Assessment Unit on 0191 445 2764 (24 hours)

Delivery Suite on 0191 445 2150 (24 hours)