Introduction of the Growth Assessment Protocol at Counties Manukau Health, New Zealand: Effect on Detection of Small for Gestational Age Pregnancy, and Maternal and Neonatal Outcomes
Cowan, Florence Joyce
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Timely identification of the small for gestational age (SGA) fetus is pivotal in high quality antenatal care. Non-detection of poor fetal growth multiplies the risk of morbidity, stillbirth, and neonatal death amongst these vulnerable pregnancies. It is crucial that the tools used for detection of SGA are effective and appropriate for the target population to modify risk by optimal management. The United Kingdom (UK) based Perinatal Institute’s Growth Assessment Protocol (GAP) is being introduced in New Zealand district health boards (DHBs), and while it has been associated with improved detection of fetal growth restriction in the UK and Australia, the programme has not been evaluated in a New Zealand, a unique setting in that antenatal care is usually provided by a single maternity provider. GAP education incorporates SGA risk selection, with specialist review and a schedule of growth scans for high risk pregnancies, serial fundal height measurement, use of customized growth standards, and an evidence-based guideline for management if SGA is detected. Counties Manukau Health (CMH) is New Zealand’s largest DHB and was the first New Zealand DHB to implement GAP. CMH serves a multi-ethnic population with high obesity and high rates of socio-economic deprivation and has the highest perinatal mortality in New Zealand. The primary objective of this thesis is to determine whether introduction of GAP at CMH has increased antenatal detection of SGA. The secondary objectives are to determine if GAP is associated with increased induction of labour, caesarean birth, and reduced composite adverse neonatal outcome (Apgar score <7 at 5 minutes, admission to the neonatal unit for >48 hours, and ventilation). A retrospective before and after study was undertaken, using routinely collected data from two 12-month epochs: pre-GAP 2012, before widespread use of any element of GAP; and post-GAP 2017, one year after introduction of GAP education. The study population comprised women with singleton non-anomalous pregnancies, booked by 20 weeks with a DHB midwife, and who gave birth after 24 weeks of gestation. At CMH, a team of DHB midwives provide continuity of antenatal and postnatal care, which is the model of care provided for pregnancies in the study. This differs from the model of care provided by community (self-employed) midwives who provide full continuity of care. Maternal and neonatal outcomes were compared in the pre- and post-GAP cohorts for pre-specified outcomes by logistic regression, with adjustment for potential confounding by factors associated with SGA, including New Zealand deprivation index, ethnicity, maternal age, body mass index (BMI) and cigarette smoking. Pre- and post-GAP cohorts were compared by non-SGA and SGA subgroups, and by SGA identification status. The difference in exposure effect between these respective subgroups was assessed by an interaction test. Antenatal detection of SGA increased significantly after introduction of GAP from 22.9% to 57.9% (aOR=4.81, 95% CI 2.82, 8.18; p<0.0001) with very similar SGA rates across epochs (13.8% vs 12.9%; p=0.68). The increase in SGA detection was greater in Maaori and Pacific Island women (pre-GAP 18.9% vs post-GAP 63.8%) compared with other ethnicities (pre-GAP 28.6% vs post-GAP 52.1%; interaction p=0.049) but was similar among BMI groups. Induction of labour and caesarean birth increased between epochs, but this increase was similar in SGA and non-SGA pregnancies. Among those with SGA, increased antenatal identification of SGA post-GAP appeared to be associated with lower composite adverse neonatal outcome (identified SGA: pre-GAP 32.4% vs post-GAP 17.5%, aOR=0.44, 95% CI 0.17, 1.15; non-identified SGA: pre-GAP 12.3% vs post-GAP 19.3%, aOR=1.81, 95% CI 0.73, 4.48; interaction p=0.03). Identification also appeared to reduce prolonged (>48 hours) neonatal unit admission (identified SGA: pre-GAP 29.4% vs post-GAP 16.3%, aOR=0.42, 95% CI 0.15, 1.15; non-identified SGA pre-GAP 9.6% vs post-GAP 15.8%, aOR=1.86, 95% CI 0.63, 5.52; interaction p=0.04). It is acknowledged that the study was undertaken by the New Zealand GAP lead educator, who recognized and managed the potential conflict of interest. In conclusion, introduction of the GAP programme in a multi-ethnic population with high obesity appeared to be associated with a 5-fold increase in likelihood of SGA detection, without increasing obstetric intervention for SGA. GAP also appeared to be associated with reduced composite adverse neonatal outcome and prolonged neonatal unit admission amongst identified SGA, which will likely result in cost savings. The detection of SGA post-GAP in the CMH community was similar to the best performing GAP units in the UK and similar to rates of detection using routine late pregnancy ultrasound scan. GAP is effective in a New Zealand setting with a continuity of care model.