I'm taking my answer from Susan E. Klepp's article "Revolutionary Bodies: Women and Fertility in Transition in the Mid-Atlantic Region, 1760-1820" The Journal of American History, Vol. 85, No. 3 (Dec., 1998), pp. 910-945. The time and place vary a bit from your question (though the author does include some words about Virginia), but I think the answers hold up.

In the early 18th century, English and American culture celebrated fertility and pregnancy. Ben Franklin's Poor Richard's Almanack" quipped that "A Ship under sail and a big-bellied Woman, /Are the handsomest two things that can be seen common." Pregnant women were frequently described as "flourishing" or with other, similarly positive adjectives. This was a boom time for British North America, with colonists flooding across the Atlantic and, unlike the 17th century, surviving long enough to reproduce. The improved diet and generally higher standard of living in America meant that a much wider section of the population could afford having multiple children, and had the physical well-being to support and raise healthy children. However, conditions in the last four decades of the century changed these patterns. War is always a difficult time to have children, and half the years between 1755 and 1785 were spent at war (and this ignores Pontiac's War and the increased raiding on the frontier that persisted after the Revolutionary War). The industrializing economy also cut back on the need for extra farm hands, and large families were a threat to wage workers even if they created more opportunities for a successful child to provide for their parents when they got old. The Revolution also gave women the opportunity to criticize a view of pregnancy that seemed to assume pregnancy was their natural and happiest state. People thus began to view pregnancy as the exception, an aberration, rather than the natural rule. Books and pens (symbols of intellectual capacity) began to replace flowers and fruits (symbols of fertility) as props in women's portraiture of this period. As an uncommon and temporary condition that limited a woman's independence, pregnancy became linked to sickness, something little discussed in public. Women also pointed to the risks inherent in childbirth as a reason to fear, and thus avoid, frequent pregnancy.

Concerns about class and race also played a role in changing attitudes towards pregnancy. Restraining one's desires and impulses became the mark of the upstainding Republican citizens in the early 19th century. Small, planned, and carefully managed families were thus the mark of sober, restrained, proper people. The poor, profligate and debauched as they were, could not be counted on to take the necessary steps to avoid pregnancy, and thus worsened their condition by popping out more mouths to feed. Black slaves were viewed as even worse, breeding (a term generally not used in regards to whites) like animals. Mix this together, particularly if you add in tightly (literally, considering the role of stays and corsets) controlled ideas of female beauty, and you have a recipe for women treating pregnancy as a sickness.

I just want to add a couple of things. The first is that while people didn't really write or speak openly about pregnancy - they used euphemisms and skirted the issue (Frances Hodgson Burnett's The Making of a Marchioness is an hilarious example; I wouldn't have known the main character was pregnant if I hadn't already seen the adaptation, The Making of a Lady) - women were not expected to hide from the moment of conception. I left several comments on an earlier, related question several months ago - specifically here, I pointed out that primary sources (even medical or legal ones) use "confinement" to refer to only the very, very end of the pregnancy and the labor.

The second is that early twentieth century perceptions of the 19th century are often exaggerated. Sometimes this was done to contrast the quaint and domestic and sweet period to the "modern" early twentieth century (similar to the way the 1950s are used today), and sometimes to contrast its perceived repression and oppression to contemporary freedom (... also similar to the way the 1950s are used today). Both come through very strongly in popular culture - books, songs, sentimental artwork, advertising. The euphemism "confinement" for labor influenced the idea that women were confined and hidden all through pregnancy - which people were not eager to discredit at the time, as it proved that the twentieth century was truly a more advanced time, since women were not confined - and can still be found repeated, unquestioned, in pop history books today.