the term "gravid" ( "burdened, heavy") is used to describe the condition of an animal (most commonly fish or reptiles) when carrying eggs internally. For example, Astatotilapia burtoni females can transform between reproductive states, one of which is gravid, and the other non-gravid. In entomology it describes a mated female insect. Parity in medicine In human medicine, parity is the number of pregnancies carried by a woman for at least 20 weeks (duration varies from region to region, 20 – 28 weeks, depending upon age of viability). If a woman carries the fetus to viable age, even if ultimately the fetus is born deceased, this still counts as an instance of parity, as parity is based on the time of gestation prior to a birth, and not the status of the offspring once born. A woman who has never carried a pregnancy beyond 20 weeks is nulliparous and is called a nullipara or para 0. A woman who has given birth once is primiparous and is referred to as a primipara or primip. A woman who has given birth two, three, or four times is multiparous and is called a multip. Grand multipara describes the condition of having given birth five or more times. Like gravidity, parity may also be counted. A woman who has given birth one or more times can also be referred to as para 1, para 2, para 3, and so on. Viable gestational age varies from region to region. Nulliparity A nulliparous () woman (a nullipara or para 0) has never given birth. It includes women who have experienced spontaneous miscarriages and induced abortions before the mid-point of pregnancy, but not women who have experienced pregnancy loss after 20 weeks. Nulliparity has been implicated in the development of various complications during pregnancy including preeclampsia, gestational diabetes and pre-term labor. Long-term and permanent nulliparity () are risk factors for breast cancer. For instance, a meta-analysis of 8 population-based studies in the Nordic countries found that never giving birth was associated with a 30% increase in the risk of breast cancer compared with women who have given birth, and for every 2 births, the risk was reduced by about 16%. Women having their first birth after the age of 35 years had a 40% increased risk compared to those with a first birth before the age of 20 years. Parity in biology In agriculture, parity in biology