Complex sentence: These conclusions have been disputed by Avraham Ebenstein, whose work finds that high male-to-female ratios occur only after the first birth, ruling out the Hepatitis B explanation, unless mothers contracted Hep B only after giving birth to their first child.
Split into simpler sentences: These conclusions have been disputed by Avraham Ebenstein, whose work finds that unnaturally high male-to-female ratios occur only for for children born after the first-born. This rules out the Hepatitis B explanation, unless mothers contracted Hep B only after giving birth to their first child.