Prediction of fecundability from semen analysis: problems in providing an accurate prognosis

Sperm protamine 1/protamine 2 ratios are related to in vitro fertilization pregnancy rates and predictive of fertilization ability

OBJECTIVE

To evaluate whether aberrant sperm P1/P2 ratios are predictive of abnormal fertilizing ability and are related to in vitro fertilization (IVF) outcome.

DESIGN

Prospective case-control study.

SETTING

University-based infertility and IVF clinic.

PATIENT(S)

Forty-three male infertility patients with an abnormally reduced P1/P2 ratio, 251 patients with a normal P1/P2 ratio, and 121 patients with an abnormally elevated P1/P2 ratio.

INTERVENTION(S)

Human IVF, the sperm penetration assay (SPA), and sperm protamine quantification via nuclear protein extraction, gel electrophoresis, and densitometry analysis.

MAIN OUTCOME MEASURE(S)

Sperm P1/P2 ratios; P1 and P2 quantities; SPA scores; and IVF-fertilization, embryo-quality, pregnancy, delivery, and spontaneous-abortion rates.

RESULT(S)

Standard IVF fertilization rates and SPA scores were significantly reduced in patients with abnormally low and high P1/P2 ratios. In vitro fertilization embryo quality was comparable between these groups, but pregnancy rates were significantly reduced in patients with abnormally reduced P1/P2 ratios.

CONCLUSION(S)

The P1/P2 ratio has a significant relationship to sperm fertilization ability. The relationship between protamines and fertilization ability is not understood but may be either a reflection of generalized abnormalities during spermiogenesis or an indication of protamine deficiency acting as a regulator or checkpoint of spermatogenesis.

Value of the hamster oocyte test and computerised measurements of sperm motility in predicting if four or more viable embryos will be obtained in an IVF cycle

The experimental group consisted of men from 81 couples waiting for in vitro fertilization (IVF), about half of whom had sperm dysfunction defined by a negative post-coital test. A diagnostic semen sample was subjected to a hamster oocyte penetration test (HOPT) after stimulation of the acrosome reaction with A23187 +/- pentoxifylline and to computerized sperm motility measurements (CASA) as well as conventional semen analysis according to the WHO protocol. Logistic regression was used to identify parameters that predicted the probability of achieving four or more viable embryos at IVF among the 65 couples from whom four or more oocytes were collected. The number of oocytes available and whether the woman had previously been pregnant (ever pregnant) were important factors but once these had been taken into account a number of sperm parameters had additional predictive power. The most useful of these were the percentage sperm static (CASA) or the percent sperm progressively motile (conventional semen analysis) in the Percoll preparation. A model incorporating the number of oocytes collected, ever pregnant and percentage sperm static achieved 85% correct prediction of outcome in the experimental dataset but only 62% correct prediction in an independent set of 280 IVF cycles. The percentage of hamster oocytes penetrated was a significant predictor but had no advantage over simple motility measurements. The results illustrate the difficulty of basing a prognosis for achieving satisfactory fertilization in IVF on the properties of spermatozoa.