Modern pregnancy tests involve peeing on a stick and waiting for the result to be revealed. Back in the day, a Dutch woman might have peed in a urinal flask and waited for the result to be revealed to the piskijker (literally, piss-looker) who was looking for either a vision of a baby or for the sediments in the urine to form the shape of a baby.
Of course, this was 100% quackery, you cannot tell if a person is pregnant by looking at (or scrying) their urine. These piskijkers were suspect even in their own time.
In the painting, a “doctor” sees a baby in the flask of the young unmarried woman’s urine. Her father looks at her in rage, while the younger boy (an a-hole younger brother perhaps?) looks at the viewer while laughing and making an obscene hand gesture.
The flask was an allegory for the uterus in birth figures (diagrams of fetal positioning), in alchemy, as well as for this pseudo-urinalysis to determine pregnancy. Alchemists considered the flask a kind of womb where alchemical reactions converted materials into new forms. In the actual womb, male and female seed was believed to combine with humoral heat to create a baby. Some alchemists were certain that if they could just find the right equation they could create artificial life in their glass wombs.
Whiteley, Rebecca. 2017. “Roy Porter Student Prize Essay Figuring Pictures and Picturing Figures: Images of the Pregnant Body and the Unborn Child in England, 1540–c.1680.” Social History of Medicine, Vol. 32(2), 241–266.