Due date is calculated from the first day of the last menstrual period—not when sex occurred

Fetal development, week by week

Gestation is the period of time between conception and birth when a baby grows inside the mother's womb. Changes occur constantly over the course of these 40 weeks. At week 17, for instance, the skeleton of a fetus begins changing from soft...

Ancient Egyptians developed the first pregnancy test—and scientists tested it in the 1960s

A papyrus from about 1350 B.C.E. discusses a test in which a woman would urinate on wheat and barley seeds over the course of several days. If the barley grows, she's having a male child; if the wheat grows, it's a female child; and if nothing grows, she's not pregnant. Scientists went on to test this theory in 1963 and found that about 70% of the time, the urine of pregnant women did promote growth whereas the urine of nonpregnant women didn't—perhaps due to estrogen levels in the urine.

Menopause is defined as 12 months without a period

Menopause is officially when a woman stops getting her period, meaning she has stopped ovulating and can no longer get pregnant. A woman has to go a full year without bleeding or spotting to know she has hit menopause.

Only about 0.0001% of sperm, on average, successfully reach the uterine cavity

We've evolved to make pregnancy a complex and difficult process. From the initial development of the blastocyst, to the energy and nutrients needed to grow a new human, our bodies are both fighting and supporting fetal development.

Lengthy incubation periods are why it’s tough to link foodborne illness to specific foods

People may not get sick from a foodborne pathogen for several days after consuming it, making it a challenge to link the illness and its cause. Factors influencing when a person starts feeling sick—even as the pathogen is multiplying in the gut—include individual variations in immune systems and gut microbiomes, what other foods are in the person’s body, and how much of the pathogen was consumed.

Advent's length varies from 21 to 28 days each year

Because Advent always begins on the fourth Sunday before Christmas, its duration varies. When Christmas falls on a Monday, Advent is unusually short, and when it falls on a Sunday, it can be nearly four full weeks long.

Gestational diabetes occurs when the body can't produce insulin during pregnancy

Globally, pregnant people are increasingly at risk to develop gestational diabetes due to rising maternal ages and obesity rates. The condition is associated with heavier fetal weight, congenital abnormalities, and perinatal mortality, which includes stillbirths and deaths of babies younger than 7 days old.

Early texts claim Jesus was conceived on the same date of his death

Though celebrations of Jesus’ birth weren’t formalized for several hundred years after he lived, it was more common to commemorate his death. Some early Church writers connected the presumed date of his death—March 25—with his conception, implying a birth date of Dec. 25.

A credit card’s grace period is a minimum of 21 days

Under federal law in the United States, an individual’s credit card payment due date must fall on the same day of each month, at least 21 days after the cardholder’s statement closing date.

Why pregnant teachers were banned from classrooms

Until the 1970s, many schools required pregnant teachers to leave the classroom by mid-term. In 1974, the Supreme Court ruled these policies unconstitutional, establishing that women could choose to keep working while pregnant.

Pregnancy makes someone more attractive to the mosquito species that transmits malaria

Research suggests that hormonal levels can affect mosquito attraction. Pregnancy, in particular, is associated with significantly increased interest from Anopheles mosquitoes, which boosts pregnant women's malaria risk.

As of 2022, scientists estimate that 117 billion people have been born on Earth

Although no demographic data exist for more than 99% of the time humans have existed, this value can be estimated by tracking approximate population sizes over different periods and the birth rates within those periods. In 2022, about 6.8% of humans that have ever been born were alive.

The presidential election process continues for weeks after Election Day

Even after a winner is projected, the election is not complete. Between Election Day and Inauguration Day, electors formally cast votes and Congress meets in a joint session to certify the results, following a constitutionally defined timeline.

Calculate the salary of a mother's work

While traditional parenting roles are changing, mothers do a ton of work at home, from cleaning and cooking to managing household finances. This quick calculator estimates the salary a mother (or caregiver) should receive based on number of...

Delays in the decay of unstable particles provide evidence for time dilation

Physicists used the muon half-life measured in labs to predict how many should reach detectors on Earth's surface after their production in collisions between atmospheric molecules and cosmic rays. Higher detection rates were consistent with a longer half-life due to slower movement through time.

Use a CD rate calculator

This CD Rate Calculator allows you to determine your interest earnings and total savings balance at CD maturity. Enter your initial deposit, your interest rate, and your term length in months or years. Click here to use it.

China has used several different calendars because of changes in government structure

For many centuries, during which China was an imperial nation, the lunar/lunisolar calendar (aka the “rural calendar”) was the basis for organizing the year. Several attempts were made over the decades to switch to the Gregorian calendar—which begins Jan. 1—but it wasn’t until the People’s Republic of China was founded in 1949 that it stuck.

The US FDA recently tried to regulate the expanded prenatal genetic tests

The agency proposed a new rule in 2023 to make it explicit that these types of tests are devices under existing law and clarify that that the agency could move to regulate them. They finalized a regulatory change in 2024 that added the words "including when the manufacturer of these products is a laboratory" to an existing law, but a federal district court vacated that edit in March 2025—returning the law to as it was before.

Recessions are often called retroactively, rather than while they’re occurring

Because recessions are recognized when a wide array of economic factors like falling GDP and high unemployment converge, they are often officially recognized after the fact.

Dozens of US women in labor turned away from hospital between 2022 and 2024

An Associated Press analysis of federal hospital investigation data concluded that more than 100 pregnant women in medical distress were turned away from emergency rooms or treated negligently since 2022.

Mifepristone, approved in 2000, is used to end early pregnancies

The drug works by blocking progesterone, a hormone that is needed to support pregnancy. Mifepristone is typically used in combination with a second drug, misoprostol, because this regimen often causes less cramping and bleeding than just using misoprostol alone.

Babies don't develop a circadian rhythm right away

Newborns don't develop circadian rhythm until they are a few months old, which helps to explain their erratic sleep schedules. When they're around three months old they begin to release melatonin, which influences sleep, and around the same time they develop more regular sleeping routines.

How to sight the new crescent moon that starts Ramadan

Ramadan doesn't begin on a fixed date. Instead, it begins when a crescent moon is visually confirmed. The Royal Museums Greenwich explains the astronomy behind the sighting, including the conditions that must be met: the sun must be below the horizon, the moon must be above it, and the two must not be within the Danjon Limit (roughly 5 to 7 degrees of separation in the sky, as shown below).

Calculate your estimated yearly dose of ionizing radiation

This calculator from the EPA provides a value in millirems—the US unit for effective dose—based on a variety of exposure parameters, including the state a user lives in and travel-related sources of ionizing radiation, such as passing through screening machines.

Unlike other bears, polar bears do not hibernate

They do not need to wait out winter because they can find enough food in the Arctic winter, using sea ice as hunting grounds. Pregnant polar bears may be mistaken for hibernating while they den for months at a time.

The hormonal disorder PCOS was renamed PMOS in 2026, a move designed to improve care and research by shifting the focus to the hormonal causes of this condition that affects 1 in 8 women.

The syncytiotrophoblast is the outer layer of the placenta and the largest human cell, spanning an area about twice that of a king-sized bedsheet.

This real-time tracking of the hantavirus cruise ship outbreak in May 2026 offers a unique glimpse into the global reach of the outbreak and whether the virus sickened passengers and their communities around the world.

Coral polyps reproduce via broadcast spawning, where entire reefs simultaneously release reproductive cells for about one hour, once a year.

For centuries, it was common to sleep in two shifts: a few hours at the beginning of the night, and a longer period beginning around midnight

Calculate how much of your tax dollars go to each federal program based on your income, filing status, and number of children

The first line of 'immortal' human cells, which can divide indefinitely and are used in scientific research, was nonconsensually taken from a Black woman.

About 12.5% of US adults experience a phobia in their lifetime, a diagnosis that hinges on the intense fear interfering with daily life and persisting for at least six months.

English mathematician Ada Lovelace wrote the first computer algorithm a century before computers existed and hypothesized that computing devices would one day be able to compose music—foreseeing the generative AI systems of today.

The first steps to rebuilding your credit score include getting to know exactly what's on your credit report and figuring out how far you are from the '700 club,' or 'good score' range.

In 2026, Finland was named the world's happiest country for the ninth consecutive year based on its wealth, social safety network, and high life expectancy, among other factors.

Scientists can determine Earth's past climate conditions by analyzing air trapped in microscopic bubbles within ice cores—columns of compressed snow layers that build up over hundreds of thousands of years.

Brandi Chastain, the star of the 1999 US victory over China in the 1999 Women's World Cup, was a last-second choice to take the penalty kick that sealed the victory.

While El Niño moves warm Pacific Ocean waters east along the equator, La Niña moves them west, shifting where rainfall will become more common for months.

The US Constitution is widely regarded as the longest-standing written national constitution still in force—see how it has influenced rights worldwide.

Stanford built a Google Maps for the Roman Empire, revealing how much it cost to travel in the ancient world

A century of Billboard issues documenting the evolution of popular music.

Domino's Pizza's 30-minute delivery guarantee was responsible for the chain's 1980s surge, but it was discontinued after the company was found liable for delivery driver accidents.

Urushiol, the oily toxin in poison ivy, can remain allergenic on clothing for years.

Explore chaos in this simulation of two double pendulums, where small differences in the release angles produce wildly different outcomes.

While atoms are normally made of protons, neutrons, and electrons, exotic ones have been built with antimatter—alternate versions of normal matter that live for fractions of a second and are about a billion times as rare.

While the first exchange-traded fund (a 'basket' of different assets that can be bought and sold on a stock exchange) in the US only launched in 1993, the global ETF market has grown to more than $10T in the short time since.

Sears sold DIY house kits starting at $600 in its famous catalog from 1908 through the 1940s, resulting in roughly 10,000 'Sears and Roebuck houses' being built.

Abraham Lincoln was almost assassinated weeks before his inauguration as he traveled from Illinois to DC through Baltimore in 1861; it took two independent claims for Lincoln to be convinced the threat was real

Objects can be 3D printed with light by projecting 2D computerized tomography (CT) scans onto rotating cylinders of resin, which solidify upon exposure.