We studied over 160,000 pregnancies to show how your postcode affects you and your baby

Where a woman lives can shape her health during pregnancy as much as her own medical history, our new study suggests.

We looked at more than 163,000 pregnancies across Melbourne and found living in a neighbourhood dominated by fast-food outlets and with few healthy food options was strongly linked to indicators of poorer health for both mother and baby.

This included the mother being overweight going into pregnancy or having gestational diabetes, and babies born much larger than average.

These not only affect women and babies around the time of pregnancy, they increase the risk of poorer health later in life.

So we need to start thinking about urban planning and access to healthy food as core public health issues that have direct impacts on health.

What we did and found

We looked at records of single births from 2020 to 2023 across Melbourne. We then linked those records to local data about neighbourhoods. Data included the density of fast-food outlets and supermarkets, walkability and liveability.

We then accounted for factors that might explain differences in the health of pregnant women and their babies. These included a woman’s age, number of previous pregnancies, whether she smoked while pregnant, and her socioeconomic status.

Our clearest finding was that areas saturated with fast-food outlets increased women’s likelihood of entering pregnancy overweight (body-mass index or BMI of 25 or more).

Entering pregnancy overweight was strongly related to developing gestational diabetes. This is when the body cannot balance the hormonal changes of pregnancy to maintain blood sugar levels in a normal range. Although gestational diabetes usually resolves after birth, it increases a woman’s risk of developing type 2 diabetes later in life and increases her child’s chance of obesity and diabetes.

A mother’s BMI of 25 or more also increased the likelihood of delivering a large-for-gestational-age baby. This is a baby larger than 90% of babies at the same stage of pregnancy. These babies are more likely to have a difficult vaginal birth, have a caesarean birth, or admission to intensive care. They also have a higher chance of obesity and metabolic disease as children and adults due to the metabolic “programming” caused by high blood sugar levels in the womb.

But neighbourhoods with more supermarkets, fresh food stores and greengrocers, and those designed with better walkability and liveability, were less likely to have women enter pregnancy overweight and develop gestational diabetes.

The different effects between neighbourhoods held even after accounting for socioeconomic status. This means neighbourhood design itself had an independent link to the health of pregnant women and their babies. But we cannot say from our study that neighbourhood design caused poorer health.

Have we seen this before?

These results build on our earlier Melbourne study of more than 31,000 births. This found postcode-level differences in women entering pregnancy overweight, developing gestational diabetes and having large babies were related to local demographics and environments.

Higher densities of fast-food outlets and fewer fresh food stores were linked with more women entering pregnancy overweight and having large-for-gestational-age births.

We also published a study earlier this year examining access to healthy and unhealthy food outlets across more than 15,000 neighbourhoods in Victoria. This enabled direct comparisons between metropolitan and regional areas.

This showed many areas on Melbourne’s urban fringe – where housing has expanded rapidly – were dominated by fast-food outlets and had relatively few supermarkets, greengrocers, fresh food stores, or butchers.

In regional Victoria, the picture was even starker, with many neighbourhoods lacking healthy food outlets within two kilometres.

The pattern isn’t unique to Melbourne. Clustering of fast-food outlets also affects suburban areas across Sydney and Perth.

Nationwide, rural communities also often struggle with limited access to healthy food, suggesting our findings have broad relevance.

Lessons for urban planning

Our research should be used to ensure we build cities that support healthy lifestyles. Possible policy solutions could include limiting the concentration of fast-food outlets, ensuring every suburb has accessible supermarkets or greengrocers, and investing in walkable infrastructure (such as paths) and outdoor recreational spaces.

The individual-level changes may seem modest – a slightly lower BMI here, a small reduction in gestational diabetes there. But across entire populations, these translate into thousands of healthier pregnancies and fewer babies starting life at a disadvantage.

The message for families

For expectant mothers, this research helps shift the focus away from individual shaming for being overweight. Rather, it’s our collective responsibility to build environments that promote healthy families.

Through better urban planning, avoiding clustering fast-food outlets in single suburbs and investing in walkable communities, we can reduce pregnancy complications and set mothers and children on healthier life paths.

This research represents collaborative work across 12 Melbourne public maternity hospitals.