Correct Answer: B. G2P1
The obstetric score (gravidity and parity) is calculated as follows: Gravidity (G) = total number of pregnancies (including current), and Parity (P) = number of deliveries after 20 weeks of gestation (viability threshold in India). Twins delivered as a single pregnancy count as ONE parity, not two. In this case: the patient is currently pregnant (1st pregnancy counted), delivered twins 4 years ago (1 delivery = 1 parity), making her G2P1. The key discriminator is understanding that parity counts deliveries, not individual babies—a twin delivery is one obstetric event. This aligns with the standard definition used in Indian obstetric practice (DC Dutta, FOGSI guidelines) where parity reflects the number of times a woman has been pregnant and delivered viable offspring, regardless of the number of fetuses delivered simultaneously.
Why the other options are wrong
A. G3P2 — This incorrectly counts the twin delivery as 2 separate parities (P2) instead of 1. While gravidity of 3 would be correct if we counted each fetus as a separate pregnancy (which we don't), the parity is fundamentally wrong. This is a common NBE trap—students mistakenly equate number of babies with number of parities. C. G2P2 — This correctly identifies gravidity as 2 (current pregnancy + past delivery) but incorrectly assigns parity as 2. The error stems from counting each twin as a separate parity event. Parity is defined by the number of deliveries after 20 weeks, not the number of infants born. A twin delivery = 1 parity. D. G3P1 — This assigns gravidity as 3, which would only be correct if we counted each fetus as a separate pregnancy—a fundamental misunderstanding of obstetric terminology. While parity of 1 is correct (one twin delivery), the gravidity is inflated. Gravidity counts pregnancies, not babies.
High-Yield Facts
- Parity counts deliveries after 20 weeks (viability threshold), not number of babies—twins = 1 parity
- Gravidity = total number of pregnancies including current; current pregnancy is always counted
- G2P1 means 2 pregnancies total (current + 1 past), with 1 delivery after viability
- Multiple births (twins, triplets) from a single pregnancy = 1 parity event, not multiple
- Miscarriage/abortion before 20 weeks does NOT count toward parity but DOES count toward gravidity
Mnemonics
G = Pregnancies, P = Parturitions (deliveries) Gravidity = all pregnancies (count current). Parity = deliveries after viability (20 weeks). Twins in one delivery = 1 parity. Use this when you see 'multiple births' in a stem. TPAL Expansion (when needed) Term + Preterm + Abortions + Living children. But for G/P scoring alone: just count pregnancies (G) and viable deliveries (P). Twins = 1 delivery.
NBE Trap
NBE pairs twin delivery with the number of babies to lure students into counting each infant as a separate parity. The trap is especially effective because students conflate "2 babies delivered" with "parity 2"—but parity is an obstetric event counter, not a baby counter.
Clinical Pearl
In Indian antenatal clinics, correctly documenting G2P1 (not G3P2) for a woman with a twin delivery history is critical for risk stratification and counseling. Twin pregnancy itself carries higher maternal morbidity; miscounting parity can lead to inappropriate risk assessment in subsequent pregnancies.
_Reference: DC Dutta's Textbook of Obstetrics, Ch. 2 (Obstetric History & Examination); FOGSI Clinical Practice Guidelines on Antenatal Care_