Table 2 Example calculations of the 4 methods for combining maternal and fetal outcomes. M, maternal; F, fetal
Method | Example Maternal outcome (M) | Example fetal outcome (F) | Method formula | Result | Assumptions | Number of studies |
|---|---|---|---|---|---|---|
Additive | 20 QALYs | 25 QALYs | M + F | 45 | • Pregnant person and fetus are separate individuals • All QALYs are equal | 31 |
Maternal disutility: maternal outcomes only | 20 life years | Lifetime maternal disutility of 0.1 | AM, where A is the maternal disutility attributable to a poor fetal outcome. | 18 QALYs | • Only maternal outcomes are included • Maternal quality of life is impacted by fetal outcomes | 5 4 further studies combined this with an additive approach |
Dual time horizon | 10 QALYs (up to 10 year time horizon) | 25 QALYs (up to lifetime horizon) | M + F | 35 QALYs | • Additive, but impact of treatment effect lasts longer for fetus than pregnant person | 3 |
Dyad | 55 life years | 76 life years | B(M + F), where B is the utility value assigned to the combination of outcomes. | In the case of brachial plexus injury: 0.6 (55 + 76) = 78.6 QALYs | • Additive on life expectancy • Fetus and pregnant person remain a lifelong dyad, rather than 2 individuals, with a constant utility | 1 |