Fimbriae (common pili) and flagella on the surface of bacterial cells. Left: dividing Shigella enclosed in fimbriae. The structures are probably involved in the bacterium's ability to adhere to the intestinal surface. Right: dividing pair of Salmonella displaying both its peritrichous flagella and its fimbriae.
Relaxin's peak is reached during the 14 weeks of the first trimester and at delivery. It is known to mediate the hemodynamic changes that occur during pregnancy, such as increased cardiac output, increased renal blood flow, and increased arterial compliance.
When Do Pregnancy Cravings Start? Although most pregnant women will have food cravings during their pregnancy, it is also equally likely that they will have food aversions. Most of the time cravings begin during the first trimester and experts think this may be due to the first wave of hormones entering the bloodstream. It is actually possible to get cravings a week after conceiving, so in some cases it can be an early sign of pregnancy.