Background and objective There can be adverse effects on health for mothers and fathers when a baby is born, but the focus on morbidity, such as depression detracts from the positive experiences of new parents. Efforts internationally to produce tools to measure postnatal health have focused on parenting stress, problems between couples and bonding. Other lengthy instruments may have limited value in clinical or research contexts.

Aim To develop and psychometrically evaluate two instruments to accurately reflect the positive and negative aspects of postnatal health for mothers (M-PHI) and fathers (F-PHI) in the first postnatal year.

Methods Two instruments were developed in four main stages: (1) Focus groups for postnatal women and questionnaire to fathers, (2) Qualitative interviews (separately for women and men), (3) Pilot survey, then main survey to 1000 women and separate survey of fathers including the 12-Item Short Form Health Survey (SF-12), Edinburgh Postnatal Depression Scale (EPDS) and Warwick-Edinburgh Mental Wellbeing Scale (WEMWBS), (4) Re-survey of mothers and fathers for completion within one week of returning the stage 3 survey questionnaire. Principal component analysis was used; internal reliability was measured using Cronbach's α; construct validity and criterion validity were tested using prehypothesised correlations with the SF-12, EPDS and WEMWBS.

Results The mother's postnatal health instrument (M-PHI) contains positive scales: relationship with baby, social support, relationship with extended family, and negative scales: control over life, mood, role transition, sleep. plus some conditional items not relevant to all women: breast-feeding, physical health problem, relationship with partner, and sexual relationship. The father's postnatal health instrument (F-PHI) contains positive scales: relationship with baby, support from partner, support from friends, role as father; and negative scales: relationship with partner, and mood. The Cronbach's α values indicating good internal reliability ranged from 0.66 to 0.87 for the M-PHI and 0.72 to 0.90 for the F-PHI; the ICCs indicating high test-retest reliability ranged from 0.67 to 0.88 (p<0.001) for the M-PHI and 0.60 to 0.88 (p<0.001) for the F-PHI. Spearman's correlation coefficients indicated the strongest positive and negative correlations with the gold standard measures for mood, role transition and control over my life, supporting construct validity and criterion validity.

Conclusions These two instruments, generated from the subjective feelings of parents have been found to be valid and reliable measures of the postnatal health of mothers and fathers in the first postnatal year. Further validation studies are recommended.