The relationship between frequency of obstetric ultrasound scans and birthplace preference – A case control study

Objective
to investigate the relationship between frequency of ultrasounds and birthplace preference.

Study design
retrospective case-control study with the number of ultrasounds as the exposure and the pregnant woman׳s preference to give birth in a low-technology setting (midwifery-led unit or home) or a high-technology setting (obstetric unit) as the primary outcome.

Sample and Setting
low-risk primigravid women receiving antenatal care at a central London academic medical centre.

Measurements
antenatal ultrasound frequency; birthplace preference at the initial pregnancy appointment (T1) and at the commencement of labour (T2); demographic data including ethnicity, index of multiple deprivation, age, and body mass index.

Findings
1100 cases were reviewed. Women received an average of 4.03 ultrasounds during their pregnancy (SD=1.96, range 2–14). The frequency of ultrasounds for women who had a low-technology T2 birthplace preference was significantly lower than for those who had a high-technology T2 birthplace preference (t=2.98, df=1098, p=0.003, r=0.1), and women who had a constant low-technology birthrate preference had significantly less ultrasounds than other women (F (3,644)=3.475, p=.02). However, within a logistic regression the frequency of ultrasound was not associated with T2 birthplace preference, after controlling for T1 birthplace preference.

Key conclusions
the findings of this investigation suggest that a preference made early in pregnancy is a greater predictor of birthplace preference than exposure to antenatal ultrasounds.

Implications for practice
further research is required to inform interventions that would encourage low-risk pregnant women to select a low-technology place of birth.