Interobserver variation in estimation of day of conception intercourse using selected natural family planning charts
Kambic, R.; Gray, R.H.
Fertility and Sterility 51(3): 430-434
1989
ISSN/ISBN: 0015-0282 PMID: 2920843 DOI: 10.1016/s0015-0282(16)60548-4Document Number: 362414
In order to study outcome of pregnancy related to timing of conception it is necessary to have both markers of ovulation and records of intercourse. Natural family planning (NFP) charts where the woman records basal body temperature (BBT) and mucus signs are ideal for this purpose. Much work has been done relating timing of BBT and mucus signs to ovulation, but very little work has been done to examine interobserver agreement on the interpretation of these signs. Four NFP experts examined 28 NFP pregnancy charts to determine the BBT rise, the mucus peak, and two most likely days of conception intercourse. The charts were selected because they provided difficulties in interpretation. The reviewers were able to agree on the most probable day of conception intercourse in 96.4% of cases, on the mucus peak in 74.1% of cases, and on the interval between the most probable conception intercourse and mucus peak in 70.4% of cases. There was poor agreement on the first day of the BBT rise (38.5%). The authors conclude that in selected difficult NFP charts, the mucus peak is a more valid indirect measure of ovulation both because it is subject to less interobserver variation and because it more closely approximates the timing of ovulation.