Maternal and child health in Australia, like most countries, has traditionally focused on health during pregnancy and in the early years of life. But this approach may be missing a key opportunity to improve pregnancy and birth outcomes.

In a series of papers published this week in The Lancet, my research team argues women’s health in the months and years before they become pregnant can impact on their health during pregnancy and the baby’s development.

We’ve long known smoking and high alcohol consumption during pregnancy increase the risk of low birthweight and pre-term birth (before 37 weeks), which is linked to higher rates of heart disease and diabetes later in life.

Our new research shows obesity and poor nutrition can also increase the risk of pregnancy complications such as gestational diabetes, high blood pressure and pre-eclampsia. Pre-eclampsia is a serious condition that causes high blood pressure and protein in the urine, and can result in impaired kidney or liver function.

Read more: Health Check: what are the risks of drinking before you know you're pregnant?

It’s therefore important to encourage women to improve their lifestyle well before they begin planning a family. In fact, this can begin in adolescence, when many unhealthy habits – such as smoking, poor diet, and alcohol consumption – begin.

Body weight

Obesity increases the risk of a number of poor outcomes. These include pregnancy complications for the mother, such as pre-eclampsia and gestational diabetes, and problems with the baby, such as a low birthweight, a high birthweight, or having congenital anomalies such as neural tube defects which affect the brain and spine.

One possible mechanism is that the mother’s obesity elevates her levels of glucose and insulin concentrations (the sugar in her blood), which drive the growth of baby while still in the womb.

Read more: Let's address the perfect storm of factors leading to obesity in disadvantaged children

About half of women of child bearing age are overweight or obese in Australia. Not only are these women at increased risk of high blood pressure, pre-eclampsia and gestational diabetes during pregnancy, but we found substantial additional risk for all women who gained weight prior to each pregnancy.

Even for women in the healthy weight range, a weight gain of more than 2.5% of their body weight prior to pregnancy was associated with 2.7-times higher risk of developing gestational diabetes compared with healthy weight women who did not gain any weight.

Diet and nutrition

Diet influences body weight and nutrition. This is not just an issue for low- and middle-income countries. Even in high-income countries, diets are typically high in refined grains and sugars but lack important nutrients such as magnesium, iodine, and vitamin D.

In the analysis of dietary data from the United Kingdom, almost all women of reproductive age had iron and folate intake levels below daily recommendations for pregnancy.

A national health survey data from Australia shows 40% of women (aged 14 to 50 years) have inadequate intake of iron.

Read more: Five ways to boost your nutrition before pregnancy

For both the UK and Australia, over nine in ten young women consume fewer than the five portions of fruit and vegetables per day – which is well below the recommended dietary guidelines.

Sometimes it’s difficult to achieve sufficient nutrient intake through diet alone. This is the case for folate, which plays a critical role in early placental and fetal development.

Taking folic acid supplements in the two to three months before and after conception results in up to 70% reduction in the risk of defects in the brain, spine, and spinal chord (with spina bifida being the most common). As a result, folic acid supplements are already part of established guidelines for women planning to have children.

Our research shows women with a healthy, balanced diet in the three years before pregnancy are less likely to get gestational diabetes, high blood pressure and pre-eclampsia during pregnancy. A balanced diet includes a high intake of fruit, vegetables, legumes, nuts, and fish, and low intake of red and processed meat.

Physical activity

Physical activity has a protective role for women and their babies. Higher amounts of exercise and physical activity before conception are linked with lower risk of pre-eclampsia and gestational diabetes.

Even four hours of brisk walking per week before pregnancy seems to lower the risk of gestational diabetes.

Yet many women of reproductive age fail to reach recommended levels of physical activity. Less that two thirds of women aged between 26-30 years get the recommended 30 minutes of physical activity per day before pregnancy.

Women need time to reach health or lifestyle objectives well before conception. Reaching a healthy body weight, in particular, may require a far longer period over months or years, rather than weeks.

Read more: Before pregnancy even starts, healthy weight in mums and dads lowers obesity risk in children

Eating healthily, being active on most days and avoiding cigarettes are three things that will improve your health at any age. And if you’re planning on having children down the track, there are advantages for them too.