Correct Answer: B. Fertilization of 2 ova released in the same cycle by sperms released at intercourse on 2 different occasion
Superfecundation is the fertilization of two ova released during the same ovulatory cycle by spermatozoa from two separate acts of intercourse occurring at different times. The key discriminating feature is two different coital events within the same menstrual cycle. When a woman ovulates, she typically releases one or more ova that remain viable for 12–24 hours. If intercourse occurs on day 1 of the fertile window and again on day 3, spermatozoa from both acts can fertilize the released ova, resulting in dizygotic (fraternal) twins with different paternity markers and potentially different gestational ages at conception. This is distinct from superfetation (fertilization of an ovum during a subsequent cycle after pregnancy is already established) and from normal dizygotic twinning where both ova are fertilized by sperm from a single coital act. In Indian obstetric practice, superfecundation is clinically significant because it can result in twins with different biological fathers—a medico-legal and social consideration. The condition is rare but documented in cases of multiple intercourse during the fertile period, particularly in populations with high coital frequency during the fertile window.
Why the other options are wrong
A. Fertilization of 2 ova released at the same time by sperms released at single intercourse — This describes normal dizygotic (fraternal) twinning, not superfecundation. While two ova are released simultaneously and fertilized, they are fertilized by spermatozoa from a single coital act, not from separate intercourse events. Superfecundation specifically requires fertilization from two different occasions of intercourse, which is the critical distinguishing feature. C. Both of the above — This is incorrect because option A describes normal dizygotic twinning (single intercourse), while option B describes superfecundation (two separate intercourse events). These are mutually exclusive definitions. Superfecundation is defined exclusively by fertilization from two different coital occasions, not by a single act. Selecting 'both' conflates two distinct biological phenomena. D. None of the above — This is incorrect because option B accurately defines superfecundation. The definition provided in option B—fertilization of two ova released in the same cycle by spermatozoa from intercourse on two different occasions—is the textbook definition used in Indian obstetric literature and international reproductive medicine. Rejecting all options ignores the correct definition.
High-Yield Facts
- Superfecundation = fertilization of multiple ova from the same cycle by sperm from two or more separate coital acts
- Superfetation = fertilization of an ovum during a subsequent menstrual cycle after pregnancy is already established (extremely rare in humans)
- Superfecundation results in dizygotic twins with different paternity and potentially different conception ages—medico-legal significance in Indian practice
- Fertile window duration is 5 days before ovulation + day of ovulation; ovum viability is 12–24 hours; sperm viability is 3–5 days
- Superfecundation is rare in humans but documented; more common in animals with polyestrous cycles and multiple matings
Mnemonics
SUPER vs SUPER SUPERFECUNDATION = SUPER-multiple ova + FECUND (fertile cycle) + DIFFERENT intercourse times. SUPERFETATION = SUPER-subsequent cycle + FETUS already present. Use: When distinguishing between two 'super-' conditions in twinning. 2-2-2 Rule for Superfecundation 2 ova released in same cycle fertilized by sperm from 2 different intercourse events. Use: Quick recall of the three defining features when seeing 'superfecundation' in a stem.
NBE Trap
NBE commonly pairs superfecundation with normal dizygotic twinning (option A) to trap students who confuse "two ova fertilized" with the actual requirement of "two separate coital events." The trap exploits incomplete understanding of the temporal distinction—students may select option A because it mentions two ova without recognizing that superfecundation specifically requires fertilization from different intercourse occasions.
Clinical Pearl
In Indian medico-legal cases involving disputed paternity in twins, superfecundation must be considered—DNA testing may reveal different biological fathers despite both twins being born from the same pregnancy. This has significant implications in inheritance, succession, and maintenance cases under Indian law.
_Reference: DC Dutta's Textbook of Obstetrics, Ch. 10 (Multiple Pregnancy); Harrison's Principles of Internal Medicine, Ch. 295 (Pregnancy and Reproduction)_