A weighty issue: The implications of an ultrasound prediction of a large baby in pregnancy

The assessment of fetal growth in Aotearoa New Zealand is governed by a largely medical model of care which highly values the purported objectivity of sonographic assessment. Ultrasound scans are an increasingly normalised part of pregnancy care, and expectant parents may advocate strongly for access to them. It could be questioned whether the increasing number of scans is aligned with clinical need. This paper presents a literature review that explores the implications of an ultrasound diagnosis of a large baby during pregnancy. Method: Databases searched were CINAHL, PubMed, Proquest, and Google Scholar. Search terms used were “macrosomia”, “large for dates” and “large for gestational age”. This search was first undertaken in May 2019, and then repeated in November 2020. Findings: Sonographic assessment of fetal size can be inaccurate and the existence of a predicted fetal weight on scan increases the likelihood of birth interventions, regardless of the baby’s actual size. While there are potentially negative outcomes associated with a larger baby, it is unclear whether birth interventions will significantly reduce the occurrence of these outcomes. There is limited research that focuses on the parents’ experience of having a predicted large baby, offering contradictory insights, which suggests the influence of conflicting meanings applied to large babies and ignoring the experiences of women whose babies were predicted to be large but were born “normal” sized. Discussion: Midwives are encouraged to openly discuss with women the limitations in available evidence in this area. Midwives can consider the context of the woman and whānau (wider family), and how they may assess risk uniquely. Finally, midwives can honour the woman and whānau as the decision-makers in their own experience. There are further opportunities for research to provide a counter-narrative to medicalising discourses about large babies, grounded in a midwifery belief in normal birth. Conclusion: Midwives and women are drawn into a risk-centric paradigm that pathologises large babies for questionable benefit. To support informed decision-making within the midwifery partnership, midwives need to critically evaluate existing research and communicate its limitations and risk-centric orientation.