Clinical Snippet 01: Suspected LGA

LGA is variably defined across guidelines: most use the 90th centile (RCOG, ACOG, FIGO, QCG), while RANZCOG C-Obs 65 defines suspected fetal macrosomia at the 95th centile. Start the counselling conversation from the 90th centile; the evidence supporting IOL applies from the 95th.

Babies come in a range of sizes. Being above the 90th centile does not automatically mean there is a problem, but it does mean the chance of certain difficulties is slightly higher, increasing further above the 95th centile.
Ultrasound estimation of fetal weight is imprecise. Both clinical palpation and ultrasound can overestimate or underestimate weight. They are most useful for ruling out macrosomia rather than confirming it.
The main concern is shoulder dystocia. This is where the baby's shoulders become stuck behind the pubic bone after the head is born. Most large babies do not experience shoulder dystocia, but the risk increases with increasing birthweight.
Serious injury from shoulder dystocia is rare. Most SD is managed without harm to the mother or baby. Possible complications include clavicle fracture, brachial plexus injury, intracranial haemorrhage, and (extremely rarely) brain injury or death.
IOL reduces composite morbidity when EFW is above the 95th centile. The DAME trial shows IOL at 37-38 weeks reduces the combined risk from ~6/100 (conservative) to ~2/100 (IOL). Around 60 women need to be induced to prevent one neonatal fracture.
The Big Baby Trial (>90th customised centile) did not demonstrate a significant reduction on ITT, though the per-protocol analysis showed benefit.
IOL does not increase the caesarean or instrumental delivery rate. There is no statistically significant difference in caesarean or instrumental delivery rates between IOL and conservative management.
Women induced for suspected LGA have a statistically significantly higher rate of spontaneous vaginal birth (DAME: 59% vs 52%, RR 1.14, 95% CI 1.01-1.29).
A larger baby increases the chance of instrumental delivery or caesarean. Vaginal birth carries risks including OASI and levator avulsion, higher with instrumental delivery (particularly forceps). Caesarean has its own risks.
Caesarean section is not routinely recommended in this weight range but remains an option the woman should be aware of.
Counselling should be non-directional and collaborative. Present the evidence clearly and support the woman's informed decision.

See also: Vaginal birth vs caesarean section (pelvic floor counselling)

Key Evidence for Clinicians

DAME Trial (Boulvain et al. 2015, n=822)
IOL at 37-38+6 weeks, EFW >95th centile. Composite outcome (SD, fracture, BPI, ICH, death): 6.1% → 2.0%. RR 0.32 (95% CI 0.15-0.71, p=0.004). No BPI, ICH, or perinatal deaths in either group.

Big Baby Trial (Gardosi et al. 2025, n=2893)
UK multicentre RCT. IOL at 38+0-38+4, EFW >90th customised centile (GROW). SD: 2.3% vs 3.1% (ITT: RR 0.75, CI 0.51-1.09, NS; per-protocol: RR 0.62, CI 0.41-0.92, significant). No neonatal benefit. No increase in OASI (3rd degree: 2.3% vs 2.2%). Fewer CS and PPH with IOL. Stopped early (futility).

Cochrane Review (Boulvain & Thornton 2023, 4 trials, n=1190)
SD reduced: RR 0.60 (CI 0.37-0.98). Fracture reduced: RR 0.20 (CI 0.05-0.79). NNT=60 to prevent one fracture. No CS difference. Acknowledged prior OASI data error; corrected RR 3.03 (CI 0.62-14.92, NS).

RANZCOG C-Obs 65 (2021)
Suspected fetal macrosomia: EFW and/or AC ≥95th centile. Shared decision-making. Elective CS considered at EFW ≥5000g (no diabetes) or ≥4500g (diabetes).

QCG IOL Guideline (2022)
Discuss IOL from 38+0 if EFW >97th centile (or 3500g ~36wk, 3700g ~37wk, 3900g ~38wk). Note: still cites uncorrected Cochrane OASI data (RR 3.70).

Consumer-Friendly Language Examples

Collaborative, non-directional counselling style. Adapt for the individual.

Opening the conversation

"The ultrasound is showing that your baby is on the bigger side. The estimated weight is tracking in the top 5 to 10% for babies at this stage of pregnancy. That doesn't necessarily mean there's a problem, but I'd like to talk you through what it means and what your options are."

Explaining shoulder dystocia

"The main thing we think about with a bigger baby is something called shoulder dystocia. This is where, after the baby's head is born, the shoulders can get a bit stuck behind the pubic bone. The midwife or doctor then needs to do some extra manoeuvres to help the baby out.

Most of the time, this works well, but occasionally the baby can get a fractured collarbone, or there can be stretching or damage to the nerves in the arm. Very rarely, if the baby is stuck for a long time, there can be more serious problems like bleeding in the brain or, extremely rarely, brain injury or death. We need to be clear that these serious outcomes are very uncommon."

Presenting the IOL option

"One option we can discuss is induction of labour. There's good research, particularly a large trial called the DAME trial, that looked at inducing labour a few weeks early for babies estimated to be in the top 5 for size. What they found was that induction reduced the combined chance of shoulder dystocia or related injuries from about 6 in 100 down to about 2 in 100.

Some women consider that to be a meaningful reduction, but as we mentioned, most of the time, shoulder dystocia doesn't result in serious harm. We believe around 60 women need to undergo induction of labour to avoid one case of fracture."

Addressing the caesarean section rate

"One of the things that often worries people about induction is whether it increases the chance of ending up with a caesarean or needing forceps or vacuum. In this situation, the research shows no increase in either. Women who were induced actually had a significantly higher chance of a straightforward vaginal birth without any assistance."

Discussing the IOL process

"If you were to go ahead with induction, the process usually involves several steps. It often starts with a balloon catheter or a medication placed into the vagina to help soften and open the cervix. Once things are progressing, your midwife or obstetrician would break the waters and, if needed, start an oxytocin drip to get the contractions going. You would be on continuous fetal monitoring throughout. It is a more medicalised process than going into labour on your own, and it's important that you feel comfortable with that."

Downsides of IOL

"Induction is not without its trade-offs. The process can be longer and more uncomfortable than spontaneous labour. Some women describe it as feeling more medicalised, and there is research suggesting that about 1.5 times as many women describe the experience of an induced birth as traumatic compared with a spontaneous birth. And there is a small possibility that induction doesn't work and you might still end up needing a caesarean."

The conservative option

"The other option is to continue with the pregnancy and wait for labour to start on its own. The chance of the composite problems we discussed is a bit higher (about 6 in 100 versus about 2 in 100 with induction), but the majority of big babies are born without complications. If you choose to wait, we will continue with regular monitoring and reassess as things progress."

Pelvic floor and mode of delivery

"It's also worth knowing that having a larger baby makes it a bit more likely that you might need some help during the birth, whether that's with a vacuum or forceps, or in some cases a caesarean. Any vaginal birth carries a small risk of injury to the pelvic floor or a tear involving the muscle around the back passage.

These risks are higher if instruments are needed, particularly forceps. A caesarean avoids pelvic floor injury but comes with its own surgical risks. I'm happy to talk through that in more detail if it's something you'd like to consider."

Inviting the patient's perspective

"There's no single right answer here. It really comes down to what feels right for you and your family. Some women feel more comfortable reducing the risk with induction, even though it means a more medicalised birth. Others prefer to wait and let things happen naturally, accepting the slightly higher risk. Some people request a caesarean section. What are your thoughts? What matters most to you in this decision?"

Documentation Template

Copy and paste into the EMR. Delete or modify sections as appropriate.

COUNSELLING: SUSPECTED FETAL MACROSOMIA / LGA CLINICAL CONTEXT As above. [Or complete: - SFH: cm - USS: date, HC: %; AC %; EFW: g, % - GDM status: screened negative / GDM on diet / GDM on insulin / not screened - Relevant history: [prior macrosomia, prior SD, BMI, parity, other] EXPLAINED ISSUE: SUSPECTED LGA - Baby's estimated weight on ultrasound is LGA range - Ultrasound estimation of fetal weight is imprecise (error margin +/- 10-15%) - Actual birthweight may be higher or lower than the estimate - Babies in this size range have a higher chance of birth-related difficulties, particularly shoulder dystocia - All vaginal births carry a risk of injury to the pelvic floor: such as anal sphincter injury or levator avulsion - Risk increases on a continuum with increasing birthweight - Planned caesarean section is the only way to avoid maternal pelvic floor risks and neonatal injuries associated with SD OPTIONS DISCUSSED Option 1: Induction of labour (IOL) at [37-38+6] weeks Evidence for IOL benefit applies from EFW >95th centile (DAME trial). At >90th centile (Big Baby Trial), ITT analysis did not show significant SD reduction. Benefits (EFW >95th centile): - 60% reduction in composite morbidity (significant SD, clavicle fracture, ICH, death) Conservative: ~3/50 (6%) vs IOL: ~1/50 (2%) (DAME trial, Boulvain et al. 2015) - Fracture risk reduced: conservative ~5/250 vs IOL ~1/250 (Cochrane, NNT=60) - No statistically significant difference in caesarean section or instrumental delivery rate - Statistically significant higher rate of spontaneous vaginal birth with IOL (DAME: 59% vs 52%, RR 1.14, CI 1.01-1.29) Risks: - Anal sphincter tears: no difference vs awaiting spont labour - More medicalised birth experience (balloon, prostaglandin, ARM, oxytocin, CTG) - Traumatic birth feelings approximately 1.5x more common with IOL vs spontaneous labour - Neonatal RDS risk with early-term birth (37-38 weeks) - Possibility of failed induction requiring caesarean section IOL process discussed: cervical ripening (balloon +/- prostaglandin), ARM, oxytocin infusion, continuous CTG monitoring Option 2: Conservative management (await spontaneous labour) Benefits: - Spontaneous onset of labour - Less medicalised birth experience - Avoids risks of early-term birth Risks: - Higher composite morbidity risk (~6/100 vs ~2/100 with IOL) - Continued fetal growth may increase birthweight further - May still require IOL for other indications (e.g. post-dates) Option 3: Elective caesarean section - Not routinely recommended at this EFW range (RANZCOG C-Obs 65). Recommend at EFW >/= 5000g (no diabetes) or >/= 4500g (diabetes) - Remains an option available to avoid maternal pelvic floor risks and neonatal injuries associated with SD - Risks and benefits of CS outlined PATIENT INTUITION, QUESTIONS AND PREFERENCES - [Document specific questions raised by the patient] - [Document values, specific concerns, or preferences expressed] DECISION AND PLAN - Decision: [IOL at [X] weeks / conservative management / elective CS / undecided, to review at next visit] - If IOL: planned date [DATE], booking arranged [yes / no] - If conservative: follow-up plan: - If undecided: next review: - Patient verbally consented to above plan +/- written consent to IOL - Written information or links provided: [specify]

RCOG	Shoulder dystocia patient information
Cochrane	IOL for suspected macrosomia (plain language)
Video	LGA counselling demonstration

Suspected LGA / Fetal Macrosomia