Human conception to birth date

The length of the average pregnancy is approximately 266 days.

As the point of ovulation is usually not known, an estimate of the birth date is made using the day of the last menstrual period.

This is usually 14 days before ovulation, so 14 days are added to the figure of 266, making a total of 280 days, or 40 weeks.

Only about 5% of women actually give birth on the date they are due.

Giraffes

Calves can be 6 feet tall and weigh 250 pounds when born. After only about an hour, the baby giraffe, encouraged by Mom, takes its first steps. They can’t run fast, and a mother giraffe is very protective.

Always on guard, she will sleep for only about 30 minutes a day, a few minutes at a time. Giraffe mothers are pregnant for about 15 months.

Elephants

Their pregnancies last 22 months, the longest for any mammal. Calves nurse for four to six years. Females will stay with their herd for the rest of their lives, while the males will eventually go off on their own.

All the females in a herd will help care for the calves, which can weigh about 200 pounds at birth. That's typically about 1/45 of what their mom weighs.

Koalas

A koala is the size of a jellybean at birth. It will spend the first six months of life tucked inside Mom’s pouch. Baby koalas, called joeys, have to develop the ability to digest the one thing they will eat: highly toxic eucalyptus leaves. When they’re born, they don’t have the necessary digestive tolerance. Mom helps them develop it by feeding them her feces.

Orangutans

The nurturing period between mother and baby is one of the longest in nature. Orangutans spend seven to nine years with their moms learning everything they need to know, like how to find food and build nests. Even after orangutans leave the nest, sometimes they will still visit their mom in the forest until they’re about 15 or 16. A mother gives birth every six to eight years. They are pregnant for 8 1/2 months. Usually a single infant is born.

Breeding like ...

A European rabbit can have more than 360 offspring in its lifetime, but only 15% will make it through the first year.

Polar bears

A pregnant polar bear gains about 200 pounds and then digs out a den in a deep snowbank in which to give birth. She will stay tucked away for three months with her newborn cubs until springtime. For the next 2 1/2 years, the cubs will stay close to Mom as she teaches them all the skills they need to live alone.

Mothers are pregnant about 195 to 265 days. There are typically two cubs per litter.

Other mammals’ gestation, newborn weight and weight as a fraction of mother’s:

Bengal tiger 103 days 2.2 pounds, 1/120

Giant panda 95-160 days 3.2 ounces, 1/900 (smallest of placental mammals)

Killer whale 457-548 days 265-353 pounds, 1/50

ANIMAL BABY NAMES

Aardvark: cub or calf

Alpaca, llama, guanaco or vicuña: cria

Anteater: pup

Ape: infant

Bat: pup

Beaver: kitten or kit

Binturong: pup or kitten

Boar: shoat, boarlet or piglet

Coyote: pup or whelp

Echidna: puggle Fox: pup, cub or kit

Goat: kid

Hare: leveret

Hedgehog: piglet or pup

Hippopotamus: calf

Horse: foal, colt (male) or filly (female)

Kangaroo: joey Mole: pup

Monkey: infant Mouse: pup or pinky

Platypus: puggle

Porcupine: porcupette

Pronghorn: fawn

Opossum: joey Otter: pup or whelp

Rabbit: kitten, kit or bunny

Raccoon: cub or kit

Rhinoceros: calf Seal: pup

Sheep: lamb Skunk: kitten or kit

Squirrel: pup, kitten or kit

Walrus: cub or pup

Wolf: cub, pup or whelp

Ant: antling Jellyfish: ephyra

Mosquito: wriggler

Mussel: glochidium Oyster: spat

Sea urchin: pluteus Spider: spiderling

FAMILY SIZE BY STATE

Families tend to be smaller in New England and larger in the Western states.

The average number of kids in each family in every state:

Number of children Out of every 10 women age 15 to 50, approximately:

• 44% have no children.

• 17% have one child.

• 22% have two children.

• 17% have three or more children.

Women who were 40-44 in 1994 were 14 percentage points more likely to be moms by age 24 than those in 2014, 53% to 39%.

Sources: Pew Research Center, American Community Survey, Centers for Disease Control and Prevention, U.S. census, National Geographic, BBC, babyanimalprints.com