Rep. Jamie Herrera Buetler, an expectant 34-year-old Republican serving her second term in the House, has learned that her baby suffers from a rare medical condition, Potter's Syndrome, which is often fatal.

Herrera Buetler, R-Wash., broke the somber news on her Facebook page this week in a joint statement with her husband.

"A few weeks ago Daniel and I excitedly announced that we are expecting our first baby later this fall. This post is to let you know about a sharp turn our journey has taken," she wrote. "At a recent, routine ultrasound appointment we received the difficult news that our baby has a serious medical condition called Potter's Syndrome."

Potter's Syndrome occurs when an unborn baby's kidneys fail to develop properly. A telltale sign of this problem occurs when the levels of fluid surrounding the fetus, known as the amniotic fluid, are insufficient.

The congresswoman, who would become just the fifth woman to give birth to a child while serving in Congress, said she sought a second opinion, but that diagnosis was "consistent with the initial news."

"There is no medical solution available to us," she wrote. "We are praying for a miracle."

In a normal pregnancy, a baby is bathed in about 800 ml of amniotic fluid at 34 weeks, a level which goes down to about 600 ml when the baby is at full term. In Potter's Syndrome, there is much less amniotic fluid because a developing baby's urine output is decreased or absent, signaling improper kidney function.

This lack of amniotic fluid can pose other issues as well because it serves an important role cushioning the baby from the walls of the uterus. Without it, the pressure exerted by the uterine wall can lead to a facial deformity characterized by widely set eyes. Potter Syndrome can also lead to abnormal limbs and lung problems at birth.

The condition is very serious, and usually deadly. While breathing issues brought about by improper lung development is the most pressing short-term issue, the long-term survival of the baby also depends on how severely impaired the kidneys are.

Last month, Hererra Buetler told ABC News that the news of her pregnancy broke through barriers that regularly divide the partisan Congress.

"The fun thing is, babies aren't partisan," Herrera Beutler said during a Mother's Day interview. "So even folks who we do not agree on policy, are so excited because they recognize that this is a great thing."

In her post, which has garnered more than 500 comments, Herrera Buetler pledges to continue working while her pregnancy plays out.

"We don't know what the future holds for our family, but we ask for your prayers and appreciate the privacy a family needs in such circumstances," she wrote. "According to the medical information and advice we've received, I will be able to continue to balance the responsibilities of an expectant mother with serving as your representative in Congress."