Medical References & Sources
Pregnancy Calculator Hub is built on established medical science. Below is an organized list of the organizations and key publications that inform our calculators, weekly content, and educational articles. We update our references when clinical guidelines are revised.
Organizations
World Health Organization (WHO)
We draw on WHO fetal growth standards for our pregnancy week-by-week content, particularly for fetal size benchmarks and weight ranges by gestational age. The WHO's global maternal health guidelines also inform our general pregnancy wellness content.
American College of Obstetricians and Gynecologists (ACOG)
ACOG is the primary clinical authority behind our due date calculator. We implement the methodology described in ACOG Committee Opinion No. 700 for LMP-based dating, and we follow ACOG guidance on exercise, prenatal care recommendations, and obstetric terminology throughout the site.
National Health Service (NHS, United Kingdom)
NHS patient guides are a key reference for our pregnancy week-by-week symptom descriptions, prenatal appointment schedules, and nutrition advice. NHS content is written for general audiences and is rigorously reviewed by clinical staff, making it an excellent model for accessible health communication.
Mayo Clinic
Mayo Clinic's pregnancy and fertility resources inform the patient-friendly explanations throughout our site, including descriptions of fetal development milestones, common pregnancy symptoms by trimester, and ovulation and fertility concepts.
American Society for Reproductive Medicine (ASRM)
ASRM guidelines inform our ovulation calculator and IVF due date calculation logic. We follow ASRM standards for the fertile window definition, ovulation prediction methodology, and IVF embryo transfer dating (Day 3 and Day 5 transfers).
Key Publications
Naegele's Rule (Historical Reference)
Franz Karl Naegele (1778–1851), German obstetrician, developed the formula that underpins LMP-based due date estimation. His rule — add 280 days (40 weeks) to the first day of the last menstrual period — remains the standard method for estimating gestational age and is the calculation engine of our Due Date Calculator, with a cycle-length adjustment applied for cycles that differ from the 28-day standard.
ACOG Committee Opinion No. 700: Methods for Estimating the Due Date (2017)
American College of Obstetricians and Gynecologists. (2017). Committee Opinion No. 700: Methods for Estimating the Due Date. Obstetrics & Gynecology, 129(5), e150–e154.
This committee opinion is the primary clinical reference for our Due Date Calculator. It endorses Naegele's Rule for LMP-based dating, outlines criteria for adjusting the EDD based on first-trimester ultrasound, and defines gestational age conventions. We display a citation to this document on our Due Date Calculator page.
ACOG Committee Opinion No. 804: Physical Activity and Exercise During Pregnancy and the Postpartum Period (2020)
American College of Obstetricians and Gynecologists. (2020). Committee Opinion No. 804: Physical Activity and Exercise During Pregnancy and the Postpartum Period. Obstetrics & Gynecology, 135(4), e178–e188.
Our pregnancy week-by-week content includes exercise and activity guidance per trimester. ACOG No. 804 provides the evidence-based recommendations we reference for safe physical activity levels, contraindications, and warning signs during pregnancy.
WHO Fetal Growth Charts (INTERGROWTH-21st)
Papageorghiou, A. T., et al. (2014). International standards for fetal growth based on serial ultrasound measurements: the Fetal Growth Longitudinal Study of the INTERGROWTH-21st Project. The Lancet, 384(9946), 869–879.
The INTERGROWTH-21st fetal growth standards, developed under WHO auspices, provide the size benchmarks (crown-rump length, biparietal diameter, femur length, estimated fetal weight) referenced in our weekly pregnancy content. These international standards reflect fetal growth in optimal health conditions across eight countries.
ACOG Practice Bulletin No. 230: Pregestational Diabetes Mellitus (2021)
Referenced in our content on pregnancy complications and prenatal care, this bulletin provides evidence-based guidance on managing diabetes during pregnancy, including monitoring recommendations relevant to our week-by-week prenatal appointment content.
A Note on Currency
Medical guidelines are periodically updated. While we review our content regularly, always verify time-sensitive clinical information with your healthcare provider and consult the issuing organization's current publications directly.
If you notice an outdated reference or factual error on our site, please let us know at hello@pregnancycalculatorhub.com. We take accuracy seriously and will investigate and correct any reported issues promptly.