Cheryl Ravelo / Reuters

Babies lie on a bed in the maternity ward of the government run Dr. Jose Fabella Memorial Hospital in Manila on June 1, 2011. The ward, the busiest in the country, sees an average of 60 births a day. The Philippines' population growth rate of around 2.0 percent is above Southeast Asia's average of around 1.7 percent, with an estimated 200 babies born every hour.

The world population is going through a growth spurt, but its pace varies widely from country to country due in large part to differences in birth rates. Some nations see declines while others see sharp increases.

The United Nations Population Fund estimates the world population will reach 7 billion on Oct. 31.

Women on average are having 2.5 babies each, according to UN data. That’s still above the population replacement level of 2.1 but just half of the five babies apiece they averaged in 1950, when the world population was 2.6 billion. It reached 6 billion in 1998.

In the Philippines, with a population of 101.8 million, the 2011 birth rate is 3.19 babies per woman, says the CIA World Fact Book. Hospitals estimate about 200 births an hour across the country.

Cheryl Ravelo / Reuters

Women await weigh-ins during prenatal checks at the Dr. Jose Fabella Memorial Hospital in Manila on June 6, 2011. The Philippines lacks a national policy on birth control and access to modern family planning methods frowned upon by the powerful Catholic Church. Those factors and others led to the country's population ballooning to more than 100 million, according to various government and private sector estimates. The Philippines is the second-most populous nation in the region after Indonesia.

Cheryl Ravelo / Reuters

A woman uses her cell phone while her baby lies on top of her inside the maternity ward of the Dr. Jose Fabella Memorial Hospital in Manila on June 1, 2011.

The world’s highest birth rate is in Niger, at 7.60 children per woman, according to the World Fact Book; the lowest is Macau, at 0.92. The United States rate is 2.06.

These rates affect a nation's population, which also changes due to longevity rates, immigration and other factors.

"Fertility begins to decline slowly in most developing countries, and then it declines fast, around three to four children, and then it slows down again," Gerhard Heilig, the UN chief of population estimates and projections, told Life's Little Mysteries.

Cheryl Ravelo / Reuters

The maternity ward of the Dr. Jose Fabella Memorial Hospital in Manila is crowded on June 1, 2011.

As the world hits a population milestone, Western Europe, Japan and Russia are experiencing low birth rates and aging populations leading to economic squeezes and population declines.

Money-tight Spain, with a 1.47 birth rate, can no longer afford $3,000-per-newborn government grants that were used to encourage families to boost the nation's birth rate.

In Japan, with a 1.21 birth rate, fewer working-age people will be around to support the elderly. Russia, at 1.42, faces a similar problem and has seen its population fall 6 percent since the mid-1990s.

Cheryl Ravelo / Reuters

A baby lies on a scale inside the maternity ward of the Dr. Jose Fabella Memorial Hospital in Manila on June 1, 2011.

China’s birth rate has fallen to 1.5 under three decades of strict family planning rules that limited urban families to one child and rural families to two.

India, the world’s second-most populous country behind China, has a 2.6 birth rate expected to keep its population rising for years to come.

- msnbc.com editors Natalia Jimenez and Jim Gold, with wire service reports.

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