Chronic hypertension (CH) complicates ≤5% of pregnancies and those entering pregnancy with a pre-existing diagnosis of type 1 diabetes mellitus (DM) or type 2 diabetes mellitus (T2DM) has a global prevalence of between 0.5% and 2.6% [1], [2], [3]. Prevalence of these conditions has increased substantially over recent decades and both continue to rise; influenced by advances in maternal age and increasing rates of obesity that often precede these conditions [1], [2], [4]. Women with CH are nearly eight times more likely to develop superimposed pre-eclampsia than those in the general population are to develop pre-eclampsia [5]. Additionally, they are at least twice as likely to experience an adverse neonatal outcome compared with the general pregnant population [5]. Those with pre-existing diabetes are four times more likely than those who do not have diabetes to experience a fetal death and as well as these obstetric and neonatal complications, both groups have a lifelong cardiovascular disease (CVD) risk [1], [5], [6], [7]. These data spotlight the importance of examining these populations to improve disease management during pregnancy and to reduce the associated short and long-term risks.

Weight management and more specifically, weight loss is recommended to hypertensive and diabetic populations for disease management [8], [9], [10]. Whilst weight loss is not advocated in pregnancy, avoiding excessive gestational weight gain (GWG) is important for all pregnant women, irrespective of body mass index (BMI), as this can lead to an increased risk of adverse pregnancy outcomes [11], [12]. Evidence suggests that for pregnant women with existing risk factors such as hypertension or diabetes additional support may be needed to help reduce excessive weight gain during pregnancy [13], [14], [15]. This is to address both the health of the pregnancy and their CVD risk where weight is a modifiable risk factor.

Lifestyle interventions in non-pregnant populations improve blood pressure control and the quality of life in hypertensive populations [16], [17], [18]. A review of 105 trials including 6805 participants found statistically and clinically significant reductions in systolic blood pressure following improved dietary intake [17]. Avoiding elevated blood pressure is of utmost importance for the health of the pregnancy but to our knowledge, the effect of lifestyle interventions on blood pressure in a pregnant population with chronic hypertension or pre-existing diabetes is unclear.

Pregnancy is often cited as a powerful ‘teachable moment’ where women are motivated to adopt risk-reducing health behaviours [19]. Systematic reviews of interventions designed to exploit this have examined the effect of lifestyle interventions in the general pregnant population [20], [21], [22] or those with overweight or obesity [23] rather than those with pre-existing conditions. An individual participant data (IPD) meta-analysis that included 12,526 women from 36 randomised controlled trials (RCT), found diet and physical activity interventions successfully reduced GWG but found no convincing evidence that interventions improve maternal and fetal outcomes. This was also observed in a subgroup analysis of 128 women with existing hypertension or diabetes. However, the focus of the review, and thus the included studies, was not pregnant women with existing conditions. Such women may benefit the most from lifestyle modification. Additionally, the effect of weight changes on blood pressure was not investigated.

This systematic review aimed to collate the evidence around lifestyle interventions during pregnancy for women with chronic hypertension and/ or pre-existing diabetes (DM and T2DM), two clinically well-defined, long-term conditions. Identifying the ‘active’ components of interventions that lead to behaviour change is vital to build knowledge, allow for accurate replication of effective interventions and subsequently, implementation into practice [24], [25]. Owing to this importance, the behaviour change techniques (BCT) utilised within the included studies were identified.

The review set out to answer the following research questions:

What evidence exists around lifestyle interventions in pregnancy for those with chronic hypertension and/ or pre-existing diabetes and what behaviour change techniques are utilised in these interventions?

What effect do lifestyle interventions in pregnancy have on gestational weight in pregnant women with chronic hypertension and/ or pre-existing diabetes?

What effect do lifestyle interventions in pregnancy have on blood pressure in pregnant women with chronic hypertension and/ or pre-existing diabetes?