Pregnant and nursing women faced severe difficulties in staying healthy; maternal mortality rates increased to approximately 41 per 1000, while simple complications such as anemia, hemorrhage and premature birth became common due to vitamin deficiency. It was estimated that the number of births declined by about 0.3 children per woman during that period. Children Children, especially those under two years old, were most affected by both the famine and the poverty of the period. The World Health Organization reported death rates for children at 93 out of every 1000, while those of infants were cited at 23 out of every 1000. Undernourished mothers found it difficult to breast-feed. No suitable alternative to the practice was available. Infant formula was not produced locally, and only a small amount of it was imported. The famine resulted in a population of homeless, migrant children known as Kotjebi. Estimated number of deaths The exact number of deaths during the acute phase of the crisis, from 1994 to 1998, is uncertain. According to the researcher Andrei Lankov, both the extreme high and low ends of the estimates are considered inaccurate. In 2001 and 2007, independent groups of researchers have estimated that between 600,000 and 1 million people, or 3 to 5 percent of the pre-crisis population, died due to starvation and hunger-related illness. In 1998, US Congressional staffers who visited the country reported that: "Therefore, we gave a range of estimates, from 300,000 to 800,000 dying per year, peaking in 1997. That would put the total number of deaths from the North Korean food shortage at between 900,000 and 2.4 million between 1995 and 1998". W. Courtland Robinson's team found 245,000 "excess" deaths (an elevated mortality rate as a result of premature death), 12 percent of the population in one affected region. Taking those results as the upper limit and extrapolating across the entire North Korean population across the country's provinces produces an upper limit of 2,000,000 famine-related deaths. Andrew Natsios and others estimated 2-3 million deaths. According to research by the U.S. Census Bureau in 2011, the likely range of excess deaths between 1993 and 2000 was between 500,000 and 600,000, and a total of 600,000 to 1,000,000 excess deaths from the year 1993 to the year 2008. Black markets At the same time, the years of famine were also marked by a dramatic revival of illegal, private market activities. Smuggling across the border