Factors

How stopping contraception and twin probability affects twin probability

Older studies are mixed and do not support a stable post-pill twin multiplier. Recent contraception cessation is not weighted in model v2.

Effect size: Not weighted vs. baseline

Last updated:

What the evidence can and cannot show

Older reports explored whether conception soon after oral-contraceptive cessation was associated with dizygotic twinning [1]. The literature is mixed, uses different comparison groups and does not establish a stable individual effect or a reliable one-to-three-cycle “window.”

A systematic review on return to fertility after contraception addresses the chance of becoming pregnant, not a causal twin effect, so it cannot justify a twinning coefficient [2]. Fertility and twinning are different outcomes.

Model v2 decision

TwinCalc removed the former ×1.2 multiplier and the question from its calculator on 10 July 2026. Legacy input values are treated as neutral. The topic remains published so readers can see what changed and why.

Do not start, stop or change contraception to try to influence twinning. Contraceptive and reproductive planning decisions should be made with a qualified healthcare professional.

Instead of applying a post-pill multiplier, review TwinCalc’s included factors .

Source

How we calculated this

See the multiplier and how this factor combines with the rest of the model.

References

  1. [1] Older epidemiological report on oral contraceptive use and twinning. (1989).
  2. [2] Girum T, Wasie A. (2018). Return of fertility after discontinuation of contraception: systematic review and meta-analysis.

Related factors

×0.70–1.20

Maternal age

Spontaneous fraternal-twin rates generally rise with age, but model v2 uses a deliberately compressed weight.

Read the deep dive
Protocol-specific

IVF & fertility treatments

Risk varies by treatment, stimulation, embryo-transfer count, age and clinic; model v2 applies no universal multiplier.

Read the deep dive
×2.0

Family history

The clearest association concerns a first-degree female relative with spontaneous fraternal twins; the questionnaire uses one broad family-history proxy.

Read the deep dive