Uitgerekende datum

Geschreven door Lisette Nijenhuis, Annemieke Verbeek
Gepubliceerd op: 12 april 2024
Laatste update: januari 2026 door Margot van Dijk

Het is een van de eerste vragen die elke zwangere krijgt: wanneer ben je uitgerekend? Die datum staat niet alleen omcirkeld in de agenda van de meeste toekomstige ouders, het is ook bepalend voor beleid rondom de bevalling (denk aan inleiden bij ‘over tijd’ gaan) – en daarom meer dan alleen een geinig weetje.

In Nederland is het sinds 2010 standaard om tussen de 10-13 weken zwangerschap een termijnecho aan te bieden om de uitgerekende datum te bepalen. Daarvoor was de zogeheten Regel van Nagaele leidend – waarbij er een rekensommetje vanaf de eerste dag van de laatste menstruatie de uitgerekende datum bepaalde.

De uitgerekende datum is gebaseerd op de aanname dat een zwangerschap veertig weken duurt (bij een vitale eenling). De uitgerekende datum is de ‘mediaan’, 50% van de vrouwen bevalt ervoor en 50% erna (dit is niet hetzelfde als het gemiddelde, hierover later meer). Slechts 5% van de zwangeren bevalt precies op de uitgerekende datum.

Kloppen die 40 weken eigenlijk wel? En hoe betrouwbaar is het vaststellen van de uitgerekende datum op basis van een echo? Daarover gaat dit artikel. Ook kijken we naar de voor- en nadelen van het hebben van een uitgerekende datum.

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