Advice for expectant mothers: Eat nutritious food, take vitamins and visit the doctor for regular checkups and ultrasound exams.
It's a regimen that Shiloh and Chesapeake adhere to strictly. They take heavy-duty supplements, have experts make ultrasound images of their babies every month and eat 25 pounds of fish every day.
O.K., that's a little more fish than the average human eats - pregnant or not. Shiloh and Chesapeake are two Atlantic bottlenose dolphins who are expected to give birth in late July or August at the National Aquarium in Baltimore.
"All of us are very excited about the calves being born together," Sue Hunter, director of animal programs, said. "The word now is 'suspense,' and we anxiously await the calves' arrival."
The father of the calves is Chinook, a 430-pound adult male on breeding loan from the Minnesota Zoo.
Aquarium veterinarians and staff have been carefully monitoring the animals, who are in good health, and say that they're "cautiously optimistic" about the pregnancies.
Their optimism is always guarded because a third of all dolphin calves do not live to one year of age, in the wild or in captivity.
"There's no room for weak babies," said Dr. Leigh Clayton, director of animal health. "They need to be able to nurse underwater and come up to breathe air. Their coordination, neurological function ... all need to be perfect."
Calves are fragile when they enter the world, dolphin keepers said. They're more susceptible to pneumonia and have weaker immune systems than juvenile dolphins. As a result, expectant dolphins are never induced into labor.
"If they gave birth in September, I wouldn't be shocked," Clayton said. "We tend to be flexible about the due date because the gestational period is just being defined for dolphins."
Dolphins typically carry their young for 10 to 12 months and reproduce every two years. Beginning in July, trainers and volunteers will monitor the expectant dolphins for eight hours a day. In mid-July, the watch will increase to 24 hours until the calves are born.
"We use our existing volunteers because we need the staffing, and it helps to get them involved," said an aquarium spokeswoman, Jen Bloomer. "But there's a possibility that something may not go well. The best-case scenario is two healthy dolphins."
Aquarium volunteers will receive background information on dolphin pregnancies and birthing signs, which include increases in respiration and defecation. Labor itself lasts from 20 minutes to two hours on average, until the calf is born tail-first.
"Newborn calves have fetal folds, or creases in the skin," said another aquarium spokeswoman, Molly Sheehan. "It's very cute."
Aquarium staffers will film the birth and hope to post the footage on their Internet blog at www.aqua.org/blog.
"We're going to do our best to tape it and catch what we can," Sheehan said.
Out of the nine calves born at the aquarium since its opening in 1990, two have died: a 10-day-old male, of bacterial meningitis; and a 4-month-old female, of pneumonia.
The female, known as Bridgit, succumbed to her infection after being roughed up by at least two grown males.
Both deaths occurred in 2004 and are consistent with mortality rate statistics, according to animal care staff.
"When one passes away, we do everything we can for that animal," said Clayton, who grew teary-eyed when she spoke of the deaths.
Survival mainly depends on the mothers, who must learn how to nurse and "swim" their calves, a term used to describe the way babies follow in their mothers' slip streams until they are able to swim on their own.
Since mothering is a learned behavior in dolphins, first-timers are paired with more experienced mothers.
Luckily for the unborn calves, Shiloh, 29, and Chesapeake, 16, have had two offspring each at the aquarium. In fact, in 1992, Chesapeake was the first dolphin born in Baltimore - and Shiloh is her mom. Aquarium staffers said Shiloh had at least one other calf before she arrived in Baltimore.
"Shiloh is a fantastic mother. She's permissive and protective of her young, which is a great balance," said a senior dolphin trainer, Beth Manning. "She's like the straight A student. Once she knows something, she knows it pat."
Chesapeake, on the other hand, has a slightly different learning style than her mother.
"She's an extremely quick learner, but can be confused later on about what she had learned," Manning said. "She's like the student who crams for the test."
Both dolphins are living in the nursing pool and assisting Jade, another mother, who gave birth to a male named Foster in September. Foster is now a playful and people-oriented calf, who eats eight pounds of fish every day.
"He will be curious of his new playmates when they arrive," said Allison Ginsburg-Kimmey, manager of dolphin training.
In the meantime, Shiloh and Chesapeake take it easy in the pool. As a dominant female, Shiloh plays with Foster and keeps the others in line, while Chesapeake would rather play with a hula hoop.