When you’re pregnant, you spend a lot of time on scales. Every doctor appointment begins with hopping (or waddling) up for a weigh-in. Health care workers then plot those numbers into a (usually) ascending curve as the weeks go by.

A morbid curiosity about exactly how enormous you’re getting isn’t what’s behind the scrutiny. Rather, the pounds put on during pregnancy can give clues about how the pregnancy is progressing.

Weight gain during pregnancy is tied to the birth weight of the new baby: On average, the more weight that mothers gain, the bigger the babes. If a mother gains a very small amount of weight, her baby is more likely to be born too early and too small. And if a mother gains too much weight, her baby is at risk of being born large, which can cause trouble during delivery and future health problems for babies.
But staying within the recommended weight range is hard. Very hard. A 2017 review of studies that, all told, looked at over a million pregnancies around the world showed that the vast majority of women fell outside the weight gain sweet spot. Twenty-three percent of those women didn’t gain enough, and 47 percent gained too much, the review, published in JAMA, shows.

But here’s the tricky part. Many studies on weight gain during pregnancy and babies’ outcomes start monitoring women who are already pregnant. That means that these studies rely on women to remember, and report correctly, their prepregnancy weight. And that might not always be accurate.

A new study offers a more nuanced look at pregnancy weight gain. The results, taken from the pregnancies of more than 1,000 Chinese women, suggest that when it comes to babies’ birth weights, the timing of maternal weight gain matters, a lot.
Overall, a woman’s weight gain during pregnancy was clearly linked to baby’s weight at birth, the researchers found. But within those 40 weeks, there were big differences. Prepregnancy weight and weight gain during the first half of pregnancy are the measurements that matter, researchers suggested in the February JAMA Pediatrics. Weight gain after 18 weeks wasn’t linked to babies’ birth weight, researchers note.

Similar results, described in PLOS ONE, come from a 2017 study of Vietnamese women: Weight gain during the first half of pregnancy had two to three times the influence on infant birth outcomes than weight gain in the second half of pregnancy. It’s worth mentioning that nearly three-quarters of the Vietnamese women gained too little weight during pregnancy. And on the whole, the Chinese women were lean before they got pregnant, scenarios that make it hard to translate those findings to women who began pregnancy overweight.

Still, the point remains that weight gain during the first half of pregnancy (and even before it) may have outsized influence on the baby’s growth. Pregnancy — and the growing baby — change so much from week 0 to week 40. It makes sense that all pregnancy weight gain isn’t all one and the same.

It’s nice to see these complexities emerge as scientists get more fine-grained data. There’s still so much we don’t know about how weight gain during pregnancy, as well as other aspects of the in utero environment, can shape babies’ future health.

For the first time, scientists may have detected hints of the universe’s primordial sunrise, when the first twinkles of starlight appeared in the cosmos.

Stars began illuminating the heavens by about 180 million years after the universe was born, researchers report in the March 1 Nature. This “cosmic dawn” left its mark on the hydrogen gas that surrounded the stars (SN: 6/8/02, p. 362). Now, a radio antenna has reportedly picked up that resulting signature.
“It’s a tremendously exciting result. It’s the first time we’ve possibly had a glimpse of this era of cosmic history,” says observational cosmologist H. Cynthia Chiang of the University of KwaZulu-Natal in Durban, South Africa, who was not involved in the research.

The oldest galaxies seen directly with telescopes sent their starlight from significantly later: several hundreds of millions of years after the Big Bang, which occurred about 13.8 billion years ago. The new observation used a technique, over a decade in the making, that relies on probing the hydrogen gas that filled the early universe. That approach holds promise for the future of cosmology: More advanced measurements may eventually reveal details of the early universe throughout its most difficult-to-observe eras.

But experts say the result needs additional confirmation, in particular because the signature doesn’t fully agree with theoretical predictions. The signal — a dip in the intensity of radio waves across certain frequencies — was more than twice as strong as expected.

The unexpectedly large observed signal suggests that the hydrogen gas was colder than predicted. If confirmed, this observation might hint at a new phenomenon taking place in the early universe. One possibility, suggested in a companion paper in Nature by theoretical astrophysicist Rennan Barkana of Tel Aviv University, is that the hydrogen was cooled due to new types of interactions between the hydrogen and particles of dark matter, a mysterious substance that makes up most of the matter in the universe.
If the interpretation is correct, “it’s quite possible that this is worth two Nobel Prizes,” says theoretical astrophysicist Avi Loeb of Harvard University, who was not involved with the work. One prize could be given for detecting the signature of the cosmic dawn, and another for the dark matter implications. But Loeb expresses reservations about the result: “What makes me a bit nervous is the fact that the [signal] that they see doesn’t look like what we expected.”

To increase scientists’ confidence, the result must be verified by other experiments and additional tests, says theoretical cosmologist Matias Zaldarriaga of the Institute for Advanced Study in Princeton, N.J. Several other efforts to detect the signal are already under way.

Experimental cosmologist Judd Bowman of Arizona State University in Tempe and colleagues teased out their evidence for the first stars from the impact the light had on hydrogen gas. “We don’t see the starlight itself. We see indirectly the effect that the starlight would have had” on the cosmic environment, says Bowman, a collaborator on the Experiment to Detect the Global Epoch of Reionization Signature, EDGES, which detected the stars’ traces.
Collapsing out of dense pockets of hydrogen gas early in the universe’s history, the first stars flickered on, emitting ultraviolet light that interacted with the surrounding hydrogen. The starlight altered the proportion of hydrogen atoms found in different energy levels. That change caused the gas to absorb light of a particular wavelength, about 21 centimeters, from the cosmic microwave background — the glow left over from around 380,000 years after the Big Bang (SN: 3/21/15, p. 7). A distinctive dip in the intensity of the light at that wavelength appeared as a result.

Over time, that light’s wavelength was stretched to several meters by the expansion of the universe, before being detected on Earth as radio waves. Observing the amount of stretching that had taken place in the light allowed the researchers to pinpoint how long after the Big Bang the light was absorbed, revealing when the first stars turned on.

Still, detecting the faint dip was a challenge: Other cosmic sources, such as the Milky Way, emit radio waves at much higher levels, which must be accounted for. And to avoid interference from sources on Earth — like FM radio stations — Bowman and colleagues set up their table-sized antenna far from civilization, at the Murchison Radio-astronomy Observatory in the western Australian outback.

Scientists hope to use similar techniques with future, more advanced instruments to map out where in the sky stars first started forming, and to reveal other periods early in the universe’s history. “This is really the first step in what’s going to become a new and exciting field,” Bowman says.

A new molecule that reveals active tuberculosis bacteria in coughed-up mucus and saliva could simplify TB diagnoses and speed up tests for detecting strains of the disease that are resistant to drugs.

This synthetic molecule is a modified version of a sugar that TB bacteria consume to help build their cell walls. The sugar is tagged with a dye that lights up under a fluorescent microscope — but only if the dye isn’t surrounded by water. Dubbed DMN-Tre, the hybrid molecule stays dark until it enters a fatty, water-repellant layer in a TB bacterium’s cell wall, where it starts to glow, researchers report online February 28 in Science Translational Medicine.
Standard tests use dyes that stain a bunch of different bacteria, so technicians have to bleach the dye off everything except the TB cells, says Sumona Datta, a tuberculosis researcher at Imperial College London not involved in the work. But that chemical washing is time-consuming and prone to error. Since DMN-Tre only glows when it’s gobbled up by TB or one of its close relatives, the molecule could offer a simpler, more reliable diagnosis, she says.
Tuberculosis killed 1.7 million people worldwide in 2016, according to the World Health Organization. And rampant resistance to drugs is making the disease harder to fight.
Chemical biologist Carolyn Bertozzi, a Howard Hughes Medical Institute investigator at Stanford University, and colleagues tested the new molecule on mucus-saliva mixtures hacked up by 16 people with tuberculosis. The molecule flagged TB microbes in the samples after a couple of hours, and it revealed similar amounts of bacteria as the standard staining technique — without the hassle of post-dye chemical washing.

“That’s pretty impressive,” says Jianghong Rao, a chemist and radiologist at Stanford not involved in the work. But DMN-Tre needs to be tested in a larger clinical trial before being ready for prime time, he says.

The new TB screening technique may also have an edge in checking whether patients respond to treatment, says Eric Rubin, a microbiologist at Harvard University. Because the molecule only lights up when eaten by healthy, hungry TB bacteria, it won’t flag microbes that have been crippled or killed by antibiotics as typical tests do. So if there are still lots of glowing microbes in phlegm from patients treated with an antibiotic, a doctor knows to try a different drug.

While current drug-resistance tests can take weeks or months, DMN-Tre reveals how drug-treated bacteria are faring within a few hours. “That’s tremendously exciting,” says Carlton Evans, also a tuberculosis researcher at Imperial College London not involved in the study. Speedy drug-resistance tests (SN Online: 12/7/14) could help researchers predict sooner which antibiotics stand the best chance of taking down TB bacteria.

Adult mice and other rodents sprout new nerve cells in memory-related parts of their brains. People, not so much. That’s the surprising conclusion of a series of experiments on human brains of various ages first described at a meeting in November (SN: 12/9/17, p. 10). A more complete description of the finding, published online March 7 in Nature, gives heft to the controversial result, as well as ammo to researchers looking for reasons to be skeptical of the findings.

In contrast to earlier prominent studies, Shawn Sorrells of the University of California, San Francisco and his colleagues failed to find newborn nerve cells in the memory-related hippocampi of adult brains. The team looked for these cells in nonliving brain samples in two ways: molecular markers that tag dividing cells and young nerve cells, and telltale shapes of newborn cells. Using these metrics, the researchers saw signs of newborn nerve cells in fetal brains and brains from the first year of life, but they became rarer in older children. And the brains of adults had none.

There is no surefire way to spot new nerve cells, particularly in live brains; each way comes with caveats. “These findings are certain to stir up controversy,” neuroscientist Jason Snyder of the University of British Columbia writes in an accompanying commentary in the same issue of Nature.